Silicone hip pad moisture permeability test: a key step to ensure comfort and quality

Silicone hip pad moisture permeability test: a key step to ensure comfort and quality
In today’s global market, silicone hip pads are favored by many international wholesale buyers for their unique comfort, durability and versatility. When these buyers choose silicone hip pad suppliers, the quality and performance of the products are their most important focus, and moisture permeability, as one of the key indicators to measure the quality of silicone hip pads, is directly related to the user’s comfort experience. This article will explore in depth the various test methods for silicone hip pad moisture permeability to help you fully understand how to accurately evaluate this important property in order to stand out in the highly competitive international market and meet the strict requirements of international wholesale buyers.

1. The concept and importance of moisture permeability
Moisture permeability refers to the ability of a material to allow water vapor to pass through its surface. For silicone hip pads, good moisture permeability is essential. When users wear silicone hip pads for a long time, human skin will continue to emit moisture. If the hip pad has poor moisture permeability, this moisture will not be effectively discharged, resulting in damp skin, which may cause discomfort, skin allergies or even more serious skin problems. On the contrary, silicone hip pads with excellent moisture permeability can transfer water vapor to the external environment in time, keep the skin dry and comfortable, and enhance the overall user experience. This not only helps to enhance the market competitiveness of the product, but also provides international wholesale buyers with better quality and more reliable product options to meet their customers’ expectations for comfort.

2. Characterization indicators of moisture permeability
Before we have a deeper understanding of the moisture permeability test method, we need to be familiar with several commonly used moisture permeability characterization indicators:
(I) Moisture permeability (WVT)
Moisture permeability refers to the mass of water vapor that passes vertically through a unit area of ​​a sample per unit time under the conditions of specified temperature and humidity on both sides of the sample. Its unit is usually grams per square meter hour (g/(m²·h)) or grams per square meter 24 hours (g/(m²·24h)). The higher the moisture permeability, the stronger the moisture permeability of the material. For example, assuming that the moisture permeability of a silicone hip pad is 5g/(m²·24h) and the other is 10g/(m²·24h), the latter allows more water vapor to pass through under the same conditions and has better moisture permeability.
(II) Moisture permeability (WVP)
Moisture permeability refers to the mass of water vapor that vertically passes through a unit area of ​​a sample per unit time under a unit water vapor pressure difference under the conditions of the specified temperature and humidity on both sides of the sample. Its unit is gram per square meter Pascal hour (g/(m²·Pa·h)). Moisture permeability reflects the moisture permeability of the material under different water vapor pressure differences, which is of great significance for evaluating the performance of silicone hip pads in actual use when facing different environmental humidity changes.
(III) Moisture permeability coefficient
The moisture permeability coefficient is the mass of water vapor that vertically passes through a unit thickness and unit area of ​​a sample per unit time under a unit water vapor pressure difference under the conditions of the specified temperature and humidity on both sides of the sample. Its unit is gram centimeter per square centimeter second Pascal (g·cm/(cm²·s·Pa)). This indicator comprehensively considers the effect of the thickness of the material on the moisture permeability, and can be used to compare the moisture permeability of silicone hip pads of different thicknesses, helping manufacturers to better optimize the selection of materials and the determination of thickness during product design and development.

3. Common test methods for moisture permeability of silicone hip pads
At present, there are many methods for testing the moisture permeability of silicone hip pads in the industry, each with its own characteristics and scope of application. The following are several common test methods and their detailed principles, operation steps and applicable scenarios:
(I) Moisture absorption (desiccant) method
Principle: This method uses the moisture absorption principle of desiccant to determine the moisture permeability of silicone hip pads. Place a specific amount of desiccant in a closed test cup, then cover the opening of the test cup with the silicone hip pad sample and seal it. Under the specified temperature and humidity conditions, the desiccant will absorb the water vapor that passes through the silicone hip pad sample. By regularly weighing the mass change of the test cup, the mass of water vapor that passes through the sample per unit area per unit time can be calculated, thereby obtaining moisture permeability indicators such as moisture permeability.
Operation steps:
Prepare desiccant: Anhydrous calcium chloride is usually used as a desiccant. Dry its particles (the particle size range is generally 0.63~2.5mm) in a 160℃ oven for 3 hours to ensure that the desiccant is completely dry and has strong hygroscopicity. After that, place about 35g of the cooled desiccant in a clean and dry test cup and shake it gently to make the desiccant surface flat and about 4mm lower than the sample placement position to form a suitable space for water vapor to penetrate and be absorbed.
Install the sample: Place the silicone hip pad sample with the test surface facing up carefully on the test cup containing the desiccant to ensure good sealing between the sample and the test cup. Usually, the sample is fixed on the test cup with a gasket press and a nut, and the connection between the sample, gasket and pressure ring is sealed from the side with vinyl tape to prevent water vapor in the outside air from entering or escaping from the gap, affecting the accuracy of the test results. At this point, a complete sample assembly is formed.
** preconditioning **: Place the assembled sample assembly in the test environment of the moisture permeability test instrument, and let the sample be tested and humidified for 1 hour under the specified temperature and humidity conditions. After the humidification is completed, take out the sample assembly and put it in a desiccator for half an hour to stabilize the quality and state of the sample. After that, put it back into the test instrument again and conduct a formal test according to the standard or agreed test time. During the test, weigh the mass of the sample assembly regularly and record the change of mass over time.
Calculation results: According to the mass change before and after the test, the area of ​​the sample, the test time and other parameters, substitute the corresponding formula to calculate the moisture permeability index such as the moisture permeability of the silicone hip pad sample. For example, if the test time is 24 hours, the sample area is 100 square centimeters, the total mass of the test cup and desiccant before the test is M1 grams, and the total mass after the test is M2 grams, then the moisture permeability WVT=（（M1-M2）×10⁴）/(100×24) g/(m²·24h), where 10⁴ is used to convert square centimeters to square meters.
Applicable scenarios: The moisture absorption (desiccant) method is suitable for testing silicone hip pad products with high moisture permeability requirements, especially when it is necessary to simulate the moisture permeability performance of the product under relatively dry environmental conditions. This method can more accurately reflect the ability of the material to prevent water vapor from entering from the outside during actual use. For example, when the user is in a dry indoor environment, the silicone hip pad needs to have a certain moisture permeability to ensure that a small amount of water vapor emitted by the skin can be discharged, while preventing the dry air from excessively absorbing skin moisture and causing skin dryness. In addition, this method is also suitable for testing the moisture permeability of thicker silicone hip pads or those with a certain waterproof coating, because it can effectively detect the actual moisture permeability of the material even in the presence of a certain water vapor barrier.
(II) Evaporation (positive cup water) method
Principle: The evaporation (positive cup water) method determines the moisture permeability of the silicone hip pad by measuring the evaporation rate of water passing through the silicone hip pad sample under specified conditions. A certain amount of water is injected into the test cup, and then the silicone hip pad sample is covered at the opening of the test cup and sealed and fixed. The positive cup of the test cup is placed in the test environment of the moisture permeability test instrument. Under the specified temperature and humidity conditions, water will continue to evaporate and diffuse through the sample into the surrounding environment. By regularly weighing the mass change of the test cup, the mass of water vapor passing through the sample per unit area per unit time can be calculated, and then indicators such as moisture permeability can be obtained.
Operation steps:
Prepare test water: According to the requirements of each standard, use a measuring cylinder to accurately inject water of the same temperature as the test conditions. For example, if the test environment temperature is 25℃, inject water at 25℃. The amount of water used is usually determined according to the specifications of the test cup and relevant standards. Generally, it is necessary to ensure that the height of the water reaches a certain proportion of the test cup, such as 1/3 to 1/2, to ensure that there is enough water to evaporate during the test process and to prevent water from overflowing the test cup.
Installation of the sample: Install the silicone hip pad sample on the test cup to ensure good sealing between the sample and the test cup. Similarly, use gaskets, press pieces and nuts to fix the sample, and check the sealing effect to prevent water from leaking from the edge or water vapor in the outside air from entering the test cup, affecting the accuracy of the test results. Place the test cup with the installed sample in the test environment of the moisture permeability test instrument.
** preconditioning**: Let the test cup balance under the specified temperature and humidity conditions for a period of time, usually about 1 hour, so that the sample and water adapt to the conditions of the test environment and reach a temperature and humidity equilibrium state. After the balance is completed, take out the test cup for initial weighing and record its initial mass M1.
Testing and weighing: Put the test cup back into the test environment and weigh it regularly according to the standard or agreed test time interval. For example, weigh it once every 24 hours and record the mass values ​​M2, M3, etc. each time. Calculate the evaporation of water based on the mass change, and then obtain moisture permeability indicators such as moisture permeability. Assuming that the test time is 24 hours, the sample area is 100 square centimeters, the initial mass is M1 grams, and the mass after 24 hours is M2 grams, then the moisture permeability WVT=（（M1-M2）×10⁴）/(100×24) g/(m²2·4h).
Result calculation: Based on the obtained data, use the corresponding formula to calculate the moisture permeability parameters such as the moisture permeability of the silicone hip pad to evaluate its moisture permeability performance.
Applicable scenarios: The evaporation (upright cup water) method is mainly used to test the ability of silicone hip pads to effectively transfer water vapor emitted by the skin to the external environment when they come into contact with the skin under normal use environment conditions. This test method simulates the moisture permeability of silicone hip pads when human skin evaporates sweat naturally, so it is suitable for evaluating the moisture permeability of most conventional silicone hip pad products in daily use scenarios. For example, for silicone hip pads used in ordinary home care, medical rehabilitation and other scenarios, this method can better reflect its comfort and moisture permeability in actual applications, helping manufacturers and buyers understand whether the product can meet the user’s comfort needs in general environments.
(III) Evaporation (inverted cup water) method
Principle: The evaporation (inverted cup water) method is similar to the right cup water method, and it also measures the moisture permeability of silicone hip pads based on the evaporation of water. The difference is that the test cup is placed upside down in this method. After a certain amount of water is injected into the test cup, the silicone hip pad sample is covered on the opening of the test cup and sealed and fixed. Then the test cup is inverted in the test environment of the moisture permeability test instrument so that the sample is in contact with the water surface. Under the specified temperature and humidity conditions, water evaporates from the test cup through the sample to the external environment. By regularly weighing the mass change of the test cup, the mass of water vapor that passes through the sample per unit area per unit time is determined, and then the moisture permeability and other indicators are calculated.
Operation steps:
Prepare test water: Use water at the same temperature as the test conditions and accurately inject an appropriate amount of water into the test cup with a measuring cylinder. The amount of water should be determined according to the specifications of the test cup and relevant standards. Generally, it is necessary to ensure that when the test cup is inverted, the water surface can fully contact the silicone hip pad sample, but it will not cause excessive water accumulation at the bottom of the test cup due to excessive water, affecting the accuracy of the test results.
Install the sample: Install the silicone hip pad sample on the test cup to ensure good sealing. Use appropriate fixing devices to firmly install the sample on the test cup to prevent water from leaking from the edge. Then place the test cup upside down in the test environment of the moisture permeability tester.
** preconditioning **: Allow the inverted test cup to balance under the specified temperature and humidity conditions for a certain period of time, such as 1 hour, so that the sample and water adapt to the conditions of the test environment. After balancing, take out the test cup for initial weighing and record the initial mass M1.
Testing and weighing: Put the test cup back into the test environment and weigh it regularly at set time intervals, such as weighing it once every 24 hours, and record the mass values ​​M2, M3, etc. each time. Calculate the evaporation of water based on the mass change to obtain moisture permeability indicators such as moisture permeability. For example, if the sample area is 100 square centimeters, the initial mass is M1 grams, and the mass after 24 hours is M2 grams, then the moisture permeability WVT=（（M1-M2）×10⁴）/(100×24) g/(m²·24h).
Result calculation: Use the measured data to calculate the moisture permeability parameters of the silicone hip pad according to the corresponding formula to evaluate its moisture permeability performance.
Applicable scenarios: The evaporation (inverted cup of water) method is suitable for testing the moisture permeability of silicone hip pads in high humidity environments, especially when simulating the situation of human sweating or being in a humid environment. When the test cup is inverted, the sample is in direct contact with the water surface, and water vapor diffuses from the side where the sample is in contact with the water to the other side, which is closer to the moisture permeability working state of the silicone hip pad when there is a lot of sweat accumulated on the skin surface in actual use. For example, in hot and humid areas or after the user performs strenuous exercise, the silicone hip pad needs to have a strong moisture permeability to quickly discharge a large amount of sweat to keep the skin dry and comfortable. This method can more realistically reflect the moisture permeability effect of the silicone hip pad in such cases, provide a basis for the performance evaluation of the product in special environments, and help manufacturers optimize product design for specific market needs and meet the performance requirements of international wholesale buyers for products in different application scenarios.
(IV) Potassium acetate method
Principle: The potassium acetate method uses the saturated water vapor pressure characteristics of potassium acetate solution to test the moisture permeability of silicone hip pads. Inject saturated potassium acetate solution into the test cup to about 2/3 of the cup height. Seal the silicone hip pad sample at the opening of the test cup, and then invert the test cup in a test tank filled with pure water. Under the specified temperature and humidity conditions, due to the difference between the water vapor pressure above the potassium acetate solution and the water vapor pressure in the test environment, water vapor will be transmitted through the silicone hip pad sample. By weighing the total mass of the test cup before and after the test, the moisture permeability index such as the moisture permeability can be calculated.
Operation steps:
Prepare potassium acetate solution: Prepare saturated potassium acetate solution according to standard requirements. Usually, a certain amount of potassium acetate is dissolved in pure water and stirred continuously until the solution reaches a saturated state, that is, potassium acetate is no longer dissolved. Ensure the purity and accuracy of the solution to ensure the reliability of the test results.
Prepare the test cup and test water tank: Pour the prepared saturated potassium acetate solution into the test cup to about 2/3 of the height of the cup. At the same time, add an appropriate amount of pure water to the test water tank to ensure that it can completely submerge the bottom of the inverted test cup.
Install the sample: Carefully seal the silicone hip pad sample at the opening of the test cup to ensure good sealing to prevent water from leaking from the edge or water vapor in the outside air from entering the test cup. Place the sealed test cup upside down in the test water tank and fix the position so that the test cup maintains good contact with the bottom of the water tank to ensure that water vapor can be transmitted smoothly through the sample during the test.
** preconditioning **: After 15 minutes of inversion, perform initial weighing and record the overall mass M1 of the test cup. This step is to make the sample and test cup initially stable in the test environment and reduce the impact of initial mass fluctuations caused by placement and operation on the test results.
Test and weighing: After that, weigh the overall mass of the test cup again at a specified time interval, such as weighing once every 30 minutes or 1 hour, and record the mass values ​​M2, M3, etc. each time. Calculate the water vapor permeation based on the mass change, and then obtain moisture permeability indicators such as moisture permeability. For example, if the sample area is 100 square centimeters, the initial mass is M1 grams, and the mass after the test time is 30 minutes is M2 grams, then the moisture permeability WVT=（（M1-M2）×10⁴）/(100×0.5) g/(m²·h).
Result calculation: Based on the measured data, the moisture permeability and other moisture permeability parameters of the silicone hip pad are calculated using the corresponding formula to evaluate its moisture permeability.
Applicable scenarios: The potassium acetate method is suitable for the accurate measurement of the moisture permeability of silicone hip pads under specific humidity conditions, especially when it is necessary to simulate the moisture permeability of materials under an environment close to saturated water vapor pressure. Since the saturated potassium acetate solution has a specific water vapor pressure, this method can provide a relatively stable high humidity test environment for testing, so it is often used to study the performance of silicone hip pads in high humidity usage scenarios, such as the moisture permeability test of silicone hip pads used in certain hot and humid environments in the medical field or in special scenarios such as food processing with strict humidity requirements. This method can more accurately assess the suitability and reliability of products in these special environments, providing international wholesale buyers with more precise product performance information to meet the needs of their specific industry customers.

4. Standards and comparison of moisture permeability test methods in various countries
Globally, different countries and regions have formulated their own standards for moisture permeability test methods, mainly including China’s national standards (GB/T), American Society for Testing and Materials standards (ASTM), Japanese Industrial Standards (JIS) and British Standards (BS). The following are common moisture permeability test methods in these standards and a brief comparison:
(I) Standards and corresponding methods
China National Standards (GB/T):
GB/T 12704.1: It specifies the method of testing the moisture permeability of textiles by the moisture absorption (desiccant) method. Its test principle and operation steps are similar to the aforementioned moisture absorption method. It is applicable to a variety of textile materials and can also be used for moisture permeability testing of similar materials such as silicone hip pads.
GB/T 12704.2: It covers two test methods, evaporation (positive cup water) method and evaporation (inverted cup water) method, providing a variety of options for testing the moisture permeability of different types of materials.
American Society for Testing and Materials Standard (ASTM):
ASTM E96 Method A: Equivalent to the moisture absorption (desiccant) method, mainly used to test the water vapor transmission performance of materials, widely used in the fields of building materials and packaging materials in the United States, and can also be used as a reference method for testing the moisture permeability of silicone hip pads.
ASTM E96 Method B: Corresponding to the evaporation (inverted cup of water) method, suitable for testing the moisture permeability of materials under high humidity conditions, and is often used in the textile, leather products and other industries in the United States.
ASTM E96 Methods C and E: Also corresponding to certain variants of the moisture absorption method and evaporation method, respectively, providing more flexible test options to meet the testing needs of different materials and application scenarios.
Japanese Industrial Standards (JIS):
JIS L 1099 A-1: ​​Corresponding to the moisture absorption (desiccant) method, used to test the moisture permeability of textiles, plays an important role in Japan’s textile and clothing industry, and is also suitable for the moisture permeability evaluation of products such as silicone hip pads.
JIS L 1099 A-2 and B-1, B-2: Corresponding to the evaporation (positive cup water) method and potassium acetate method, respectively, they provide a variety of test methods for testing materials with different characteristics, and are widely used in the fields of material research and quality inspection in Japan.
British Standard (BS):
BS 7209: specifies the method of testing the moisture permeability of textiles by the evaporation (positive cup water) method, which is widely used in the quality inspection of textiles and related products in the UK, and can also provide reference for the moisture permeability test of silicone hip pads.
(II) Comparison
Differences in test conditions: There are differences in the test conditions specified in different standards. For example, in terms of temperature, the test temperature of the moisture absorption method specified in GB/T 12704.1 is generally 25℃, while the test temperature of ASTM E96 method A may vary in a wide range, such as 23℃ to 27℃, depending on the material and application scenario. In terms of humidity conditions, the humidity of the moisture absorption test environment of JIS L 1099 A-1 is usually around 40% RH, while the test humidity of GB/T 12704.1 may be 65% RH, etc. These different test conditions will lead to different test results of the same material under different standards, so the impact of test conditions needs to be considered when comparing different test results.
Different test methods have different focuses: the moisture absorption (desiccant) method is mainly used to test the moisture permeability of materials in a dry environment and the ability to prevent water vapor intrusion; the evaporation (positive cup of water) method focuses on simulating the ability of materials to discharge internal water vapor under normal use; the evaporation (inverted cup of water) rule is closer to the moisture permeability of materials when they are in direct contact with water in a high humidity environment; the potassium acetate rule provides a method for testing moisture permeability under specific high humidity conditions. The test methods included in different standards have different focuses and are suitable for different application scenarios and material property evaluation needs.
Differences in data expression: The data expression of moisture permeability test results in standards of various countries is also different. For example, GB/T standards usually characterize the moisture permeability of materials with indicators such as moisture permeability (WVT), moisture permeability (WVP) and moisture permeability coefficient, and specify their respective calculation formulas and units; ASTM standards also use similar data expressions, but there may be differences in unit conversion and significant digit processing; JIS standards, in addition to providing conventional indicators such as moisture permeability, also provide detailed requirements for the accuracy and repeatability of test results in some methods to ensure the reliability and comparability of test data. These differences may bring certain communication costs to international trade and quality inspection. Therefore, when communicating with buyers or suppliers in other countries, it is necessary to clarify the standards and data expressions used to avoid misunderstandings and disputes.
In practical applications, the choice of which standard to use for moisture permeability testing of silicone hip pads usually depends on the target market and customer requirements of the product. If the product is mainly for the Chinese market, then China’s national standards (GB/T) should be used for testing first to meet relevant domestic quality standards and regulatory requirements; for silicone hip pads exported to the United States, it is recommended to test them according to ASTM standards, because the U.S. market has a high acceptance of this standard and the United States has a large technical and market influence in this field. The use of ASTM standards can better align with local quality inspection systems and industry specifications, and improve product recognition and competitiveness in the U.S. market; if the product is exported to Japan, it should be tested in accordance with Japanese Industrial Standards (JIS) to meet local market access requirements and quality inspection specifications to ensure that the product can be smoothly sold and used in the Japanese market; for products exported to the United Kingdom and other European countries, British Standards (BS) and other relevant European standards (such as EN standards) have important reference value. Testing using these standards will help promote products in the European market and meet local quality supervision requirements. In addition, the characteristics of the product and the purpose of the test should be considered comprehensively. For example, for some high-end silicone hip pad products with extremely high requirements for moisture permeability, it may be necessary to use multiple standards for testing at the same time to comprehensively evaluate the performance of the product and meet the strict requirements of different customers and application scenarios, so as to establish a good product image and quality reputation in the international market and attract more attention and trust from international wholesale buyers.

5. Influencing factors and control points of moisture permeability test results
In order to ensure the accuracy and reliability of the moisture permeability test results of silicone hip pads, various influencing factors must be strictly controlled during the test. The following are some of the main influencing factors and corresponding control points:
(I) Test environment conditions
Temperature control: Temperature has a significant effect on the diffusion rate of water vapor. Generally speaking, as the temperature increases, the kinetic energy of water vapor increases and the diffusion rate accelerates, which may lead to an increase in moisture permeability. Therefore, the test must be carried out strictly in accordance with the temperature conditions specified in the selected test standard, and the temperature of the test environment must be stable and uniform. For example, when using the GB/T 12704.1 standard for moisture absorption test, the test environment temperature is required to be (25±1)℃. The test laboratory should be equipped with high-precision temperature control equipment, such as a constant temperature and humidity test chamber, and the equipment should be calibrated and maintained regularly to ensure the accuracy and stability of temperature control. At the same time, during the test, avoid external factors (such as direct sunlight, heat source radiation, etc.) from interfering with the test environment temperature to ensure that the temperature fluctuation is within the allowable error range. Humidity control: Humidity is also a key factor affecting the test results of moisture permeability. In the test environment, the relative humidity directly affects the partial pressure difference of water vapor, which in turn affects the rate at which water vapor passes through the silicone hip pad. For example, in the evaporation (positive cup water) method test, higher ambient humidity will reduce the water vapor pressure difference inside and outside the test cup, thereby reducing the evaporation rate and moisture permeability of water. Therefore, the relative humidity of the test environment must be accurately controlled to meet the standard requirements. For example, the ambient humidity of the evaporation (inverted cup water) method test specified in ASTM E96 Method B is generally (50±5)% RH. In addition to using equipment such as a constant temperature and humidity test chamber to control humidity, humidity sensors and monitoring equipment must be calibrated regularly to ensure the accuracy of humidity data. In addition, frequent opening and closing of the test equipment or laboratory door should be avoided during the test to prevent the influx or loss of external moisture from having a significant impact on the humidity of the test environment, resulting in deviations in the test results.
(II) Sample preparation and processing
Sample representativeness: The selected silicone hip pad samples must be well representative and can truly reflect the overall quality level and moisture permeability of the product. When sampling, multiple samples should be randomly selected from the same batch of products, and it should be ensured that the appearance of the samples has no obvious defects (such as creases, holes, uneven coating, etc.), and the size meets the test requirements. For example, if the test standard requires the diameter of the sample to be 100mm, a special sampler should be used to randomly cut out multiple circular samples with a diameter of 100mm from different parts of the silicone hip pad, and the appearance and size of these samples should be strictly checked, and samples that do not meet the requirements should be eliminated to ensure that the test results can accurately represent the moisture permeability of the batch of products.
Sample pretreatment: Before testing, samples usually need to be pretreated, such as humidity balance. Place the sample under the specified temperature and humidity conditions for a certain period of time for pretreatment to achieve a hygroscopic equilibrium state, so as to eliminate the influence of moisture differences that may occur during storage and transportation on the test results. For example, according to GB/T 12704.2, the sample needs to be pretreated in an environment of (25±2)℃ and (65±2)% RH for more than 24 hours before testing. During the pretreatment process, the sample should be placed in a well-ventilated and non-squeezed environment to ensure that each sample can fully contact the ambient air and achieve moisture balance. At the same time, record the time and conditions of the pretreatment to ensure the standardization and repeatability of the pretreatment process.
(III) Accuracy and calibration of test equipment
Accuracy of weighing equipment: During the moisture permeability test, the mass change of the test cup needs to be accurately weighed, so the accuracy of the weighing equipment is crucial. A high-precision electronic balance is one of the key instruments to ensure the accuracy of the test results. For example, in test methods such as moisture absorption (desiccant) method and evaporation (positive cup water) method, the mass change may be only a few milligrams to tens of milligrams, so the accuracy of the electronic balance used should be at least 0.1mg to ensure that the small mass change can be accurately measured, thereby improving the calculation accuracy of indicators such as moisture permeability. At the same time, the electronic balance should be calibrated and maintained regularly, and calibrated with standard weights to ensure the accuracy and reliability of its weighing results. In addition, during the weighing process, the influence of factors such as airflow and vibration on the balance should be avoided to ensure the stability and quietness of the weighing environment.
Calibration of temperature and humidity test equipment: As mentioned above, the accuracy and stability of temperature and humidity control equipment directly affect the compliance of the test environment conditions. Therefore, temperature and humidity test equipment such as constant temperature and humidity test chambers must be calibrated regularly, and temperature and humidity standard equipment that has been certified by metrology must be used for comparative verification to ensure that the temperature and humidity values ​​displayed by the test equipment are consistent with the temperature and humidity values ​​in the actual environment. At the same time, check whether the refrigeration, heating, humidification and dehumidification systems of the equipment are operating normally, and promptly discover and solve equipment failures to ensure the stability and precise control of temperature and humidity conditions during the test.
(IV) Standardization of test operation
Installation operation: When installing the sample and the test cup, the operating steps specified in the standard must be strictly followed to ensure the sealing and accuracy of the installation. For example, in the moisture absorption (desiccant) method, the amount of desiccant, the distance between the sample and the desiccant, and the flatness of the sample installation all have an important impact on the test results. It should be ensured that the amount of desiccant meets the standard requirements (such as about 35g), the sample and the surface of the desiccant are kept at a distance of about 4mm, and the sample is installed flat without wrinkles to avoid uneven air layers or direct contact between the sample and the desiccant due to improper installation, thereby affecting the transmission path of water vapor and the accuracy of the test results. At the same time, during the installation process, the action should be gentle to avoid unnecessary damage or deformation to the sample, ensuring the integrity of the sample and the effectiveness of the test.
Control of test time: The length of the test time will also affect the test results of moisture permeability. Different test standards have different regulations on test time, and usually a certain period of testing is required to ensure the stability and representativeness of the data. For example, the test time of the moisture absorption method in GB/T 12704.1 is generally 24 hours or longer, while the test time of the evaporation (positive cup water) method may be between 24 and 72 hours depending on the moisture permeability of the sample. During the test, the test time specified in the standard should be strictly followed to avoid ending the test too early or too late, resulting in inaccurate or unrepresentative data. At the same time, during the test, the specific time of each weighing should be recorded to ensure the consistency of the test time interval to improve the reliability and repeatability of the test results.
In addition, other factors such as the cleanliness of the test cup, the purity and activity of the desiccant, and the purity of water will also have a certain impact on the test results. Before the test, the test cup should be carefully cleaned to avoid residual impurities from interfering with the water vapor permeation process; ensure that the purity of the desiccant meets the standard requirements and fully dry and activate it before use to ensure its moisture absorption performance; use pure water or deionized water as test water to prevent impurities in the water from affecting the evaporation and moisture permeation process of water vapor, thereby ensuring the accuracy and reliability of the moisture permeability test results.

6. How to choose a suitable moisture permeability test method
Faced with so many moisture permeability test methods and standards, as a manufacturer or quality inspector of silicone hip pads, how to choose a suitable test method becomes the key to ensure product quality and meet customer needs. The following are some of the main factors to consider when choosing a moisture permeability test method:
(I) Product application scenarios
Daily use scenarios: If the silicone hip pad is mainly used for daily scenarios such as general home care, comfortable support for sedentary office workers, etc., then the evaporation (full cup of water) method may be a more appropriate choice. Because in this scenario, the user’s activity is relatively small and the amount of sweating on the skin is moderate, the evaporation (full cup of water) method can simulate the ability of the silicone hip pad to discharge the water vapor emitted by the skin under normal ambient humidity. Its test results can better reflect the moisture permeability of the product in daily use, helping manufacturers ensure that the product can meet the comfort needs of most daily users.
High humidity or sports scenarios: For silicone hip pads used in hot and humid areas or for sports rehabilitation and other scenarios, the evaporation (inverted cup of water) method or potassium acetate method may be more applicable. In these scenarios, the user sweats a lot and the humidity on the skin surface is high. The silicone hip pad needs to have stronger moisture permeability to cope with the discharge of a large amount of sweat. The evaporation (inverted cup of water) method can simulate the moisture permeability under such high humidity conditions, while the potassium acetate method provides a test environment close to the saturated water vapor pressure. The moisture permeability data obtained by these two methods can more accurately evaluate the performance of the product in special usage scenarios, provide more targeted guidance for product design and improvement, so as to meet the user’s comfort needs in special environments and improve the market competitiveness of the product.
(II) Customer requirements and market standards
Requirements of international wholesale buyers: Different international wholesale buyers may have different requirements for the moisture permeability test method of silicone hip pads based on the laws and regulations, industry standards and their own quality control systems in their countries. For example, US buyers may prefer to use ASTM standards for testing. Therefore, when working with customers in the US market, priority should be given to using test methods in relevant standards such as ASTM E96, such as Method B (evaporation (inverted cup of water) method), etc., to meet their requirements for product quality and test reports, smoothly enter the US market and establish a long-term and stable cooperative relationship.
Target market standards: If the product is mainly exported to the European market, then British Standards (BS) and other relevant European standards (such as EN standards) need to be focused on. For example, the evaporation (positive cup of water) method specified in British Standard BS 7209 has a high degree of recognition in the quality inspection of European textiles and related products. Testing using this standard will help products meet the quality specifications and access requirements of the European market, improve the acceptance and competitiveness of products in the European market, and promote product sales and promotion.
(III) Material properties
Thickness and density: For thicker or denser silicone hip pads, the moisture absorption (desiccant) method may be more suitable. Because thicker materials may have greater resistance to water vapor penetration, the moisture absorption method can more accurately detect small changes in water vapor penetration through the material in a dry environment, thereby evaluating its moisture permeability. For example, some silicone hip pads with thicker cushioning layers used in medical devices have relatively low moisture permeability. The moisture absorption method can be used to measure their moisture permeability under low water vapor pressure difference conditions, providing more accurate data for product quality control.
Surface treatment and coating: If the silicone hip pad undergoes special surface treatment or coating processes to give it certain special properties (such as waterproof, antibacterial, etc.), it may affect its moisture permeability. In this case, it is necessary to select an appropriate test method based on the characteristics of the surface treatment and the properties of the coating. For example, for silicone hip pads with a waterproof coating, the evaporation (positive cup water) method may be hindered by the coating, resulting in a low test result, while the moisture absorption method may be able to better reflect the material’s ability to prevent water vapor intrusion in a dry environment. Alternatively, depending on the moisture permeability characteristics of the coating, other specialized test methods or appropriate modifications to the standard methods may be required to accurately evaluate its moisture permeability and ensure that the product can maintain good moisture permeability while meeting special performance requirements and meet the user’s comfort expectations.
(IV) Test cost and time
Cost budget: Different moisture permeability test methods differ in terms of equipment purchase, consumables use, and operation complexity, resulting in different test costs. For example, the equipment required for the moisture absorption (desiccant) method is relatively simple, mainly desiccant, test cup, and weighing equipment, and the test cost is relatively low; while the potassium acetate method requires the use of potassium acetate chemical reagents and specific test water tanks and other equipment, and the cost is relatively high. When choosing a test method, you need to make a reasonable choice based on your own cost budget. For some small manufacturers or start-ups, if the cost budget is limited and the product does not have extremely high requirements for moisture permeability, they can choose low-cost test methods such as the moisture absorption (desiccant) method for quality control; while for large enterprises or high-end product manufacturers with strict requirements on product quality, in order to more comprehensively and accurately evaluate the moisture permeability of the product, even if the test cost is high, they may choose multiple test methods for comprehensive testing.
Time requirement: Test time is also one of the factors to be considered when selecting a moisture permeability test method. Some test methods have a long test cycle, such as the moisture absorption (desiccant) method and the evaporation (positive cup water) method, which usually takes 24 hours or more to obtain stable and reliable data; while the potassium acetate method has a relatively short test time, which can generally be completed within a few hours. If the company needs to get test results quickly during product development or quality control in order to adjust the production process in time or respond to urgent orders from customers, it may be more appropriate to choose a method with a shorter test time. However, it should be noted that methods with shorter test time may not fully reflect the changes in the moisture permeability of materials during long-term use in some cases. Therefore, when choosing, it is necessary to weigh the relationship between test time and representativeness of results, and make decisions based on specific project needs and time requirements.

VII. Actual test case analysis
In order to more intuitively demonstrate the application of different moisture permeability test methods in silicone hip pad testing and the difference in results, the following provides an actual test case analysis:
(I) Test background
A silicone hip pad manufacturer has developed a new type of high-elastic silicone hip pad, mainly for the medical rehabilitation market, for hip support of long-term bedridden patients and postoperative rehabilitation patients to prevent pressure sores and provide a comfortable use experience. The manufacturer hopes to evaluate the moisture permeability of the product to ensure its applicability and comfort in medical environments.
(II) Selection of test methods
Based on the product application scenario (medical rehabilitation, patients may stay in bed for a long time, and their skin is susceptible to moisture and causes pressure sores) and the target market (mainly Europe and Japan), the manufacturer chooses to use the following three test methods for moisture permeability testing:
Moisture absorption (desiccant) method: Tested in accordance with GB/T 12704.1 standard to evaluate the product’s moisture permeability in a dry environment and its ability to prevent the entry of external water vapor, simulating the use of dry environments in medical rooms in winter.
Evaporation (pour cup water) method: Tested in accordance with ASTM E96 method B, used to evaluate the product’s moisture permeability in a high humidity environment (such as in summer or when the patient sweats a lot), simulating the moisture permeability of the silicone hip pad after the patient sweats.
Potassium acetate method: Tested in accordance with JIS L 1099 method B-1 to further verify the product’s moisture permeability under conditions close to saturated water vapor pressure, meet the strict requirements of the Japanese market for product quality, and provide data support for the product to enter the Japanese market.
(III) Test results and analysis
Results of the moisture absorption (desiccant) method: The test results show that the moisture permeability of the silicone hip pad is 3.5g/(m²·24h). This result shows that in a dry environment, the product has a certain moisture permeability, which can effectively prevent the dry air from the outside from excessively absorbing moisture from the skin, while allowing a small amount of water vapor emitted from the skin to be discharged, which helps to maintain the patient’s skin moderately moist and reduce the discomfort and risk of pressure sores caused by dry skin.
Results of the evaporation (pour a cup of water) method: The moisture permeability measured by this method is 12.8g/(m²·24h). This shows that under high humidity conditions, such as when the patient sweats a lot, the silicone hip pad can quickly discharge sweat from the skin surface, keep the skin dry, reduce the possibility of pressure sores caused by long-term contact with the skin in a humid environment, and meet the high requirements of patients for the moisture permeability of hip pads in medical rehabilitation scenarios.
Results of the potassium acetate method: The moisture permeability is 10.2g/(m²·24h). The results show that the product still has good moisture permeability in an environment close to saturated water vapor pressure, which further verifies its applicability in special high-humidity medical environments (such as hot and humid rehabilitation treatment rooms, etc.), meets the strict quality and performance standards of the Japanese market for medical supplies, and provides strong technical support for the export of products to the Japanese market.
(IV) Comprehensive conclusion and application
By comparing the results of three different test methods, the manufacturer draws the following comprehensive conclusions:
The new silicone hip pad has good moisture permeability under different environmental conditions, and can meet the performance requirements of the medical rehabilitation market for product comfort and prevention of pressure sores.
The results of different test methods complement each other and fully reflect the moisture permeability performance of the product in various actual use scenarios. The results of the moisture absorption (desiccant) method prove the applicability of the product in a dry environment; the evaporation (inverted cup of water) method and potassium acetate method highlight its advantages in a high-humidity environment, providing comprehensive data support for the market promotion and application of the product.
Based on these conclusions, the manufacturer decided to promote the product to the European and Japanese markets, and listed the results of the three test methods in detail in the product promotion materials and quality reports to enhance the trust and recognition of international wholesale buyers in product quality. At the same time, these test results also provide important references for subsequent product improvements and research and development. For example, manufacturers can further optimize the formula and production process of silicone materials based on test data to improve the product’s moisture permeability to meet higher standards of market demand and customer expectations.

7. Summary
As a key performance indicator of silicone hip pads, the accuracy and reliability of its test method are directly related to the product’s quality assessment and market competitiveness. By deeply understanding the concept of moisture permeability, characterization indicators, and the principles, operating steps and applicable scenarios of various test methods, manufacturers can better choose appropriate test methods to evaluate the product’s moisture permeability and ensure that the product can meet the user’s comfort needs in different application scenarios. At the same time, being familiar with the standards and comparisons of moisture permeability test methods in various countries will help companies establish effective communication and cooperation with international wholesale buyers in the global market and meet the quality standards and customer requirements of different countries and regions.
In addition, strictly controlling the influencing factors in the moisture permeability test process, such as test environment conditions, sample preparation and processing, test equipment accuracy and calibration, and the standardization of test operations, is an important guarantee for obtaining accurate and reliable test results. Through the analysis of actual test cases, we further see the complementarity and importance of different test methods in evaluating the moisture permeability of silicone hip pads, which provides companies with valuable practical experience in product research and development, quality control and market promotion.