Water Vapor Transmission Test ASTM E96

In this article,  we will talk about the Water Vapor Transmission Test ASTM E96. You will learn about the water vapor transmission rate of materials (WVTR). It can be checked using desiccant and water methods. Testing conditions greatly influence this test method as they greatly influence results. You will also learn how to perform ASTM E96 in a textile lab.

WVTR (Water Vapor Transmission Rate)

It is also known as Moisture Vapor Transmission Rate (MVTR). The thermal properties of textile garments depend primarily on the textile’s capacity to transmit water vapors. A high degree of water vapor permeability in a garment increases the movement of water vapor from the skin through the breathable fabrics into the surrounding environment, particularly during training sessions or in hot environments. The discomfort due to dampness and sweaty skin may appear if there is a blockade to the dispersion of water vapor. WVTR test is widely used in packaging, food, pharmaceutical, textile, and construction industries.

ASTM E96

In the fabric testing laboratory, this test is used to evaluate the breathability of fabrics. The quantity of water vapors that can pass through the fabric in a specific time and temperature shows its breathability. It is used to make a garment more comfortable for the wearer. Breathable fabrics are essential for athletes as they are required to maintain their body temperature by evaporating their sweat.

ASTM E96 method a vs b

There are two ways to determine WVTR by ASTM E96. Both methods require a controlled environment.

ASTM E96 Method A – Desiccant Method

In this method, the sample is placed in a dish that contains a desiccant. The whole apparatus is weighed and then placed in a controlled environment.  The low vapor pressure in the dish due to desiccant creates a pressure difference and allows moisture to pass through the sample. This movement of water vapors increases the weight of the apparatus, which is measured periodically with time. A graph between mass and time is formed as the equilibrium stage occurs.

ASTM E96 Method B – Water Method

This is the opposite process compared to the desiccant method. It also has the same principle of pressure difference. In this process, the dish contains water and a sample and is placed again in a controlled environment. Gradually, moisture moves away from the dish, and the weight of the apparatus decreases. The weight of the apparatus is measured with time, and a graph is formed.

Apparatus for ASTM E96

• Water Vapor Permeability Tester
• Weight Balance
• Desiccant (Anhydrous Calcium Chloride)
• Distilled Water (For Water Method)

Test Conditions – Temperature and Relative Humidity

Temperature should be maintained at 38°C throughout the test, while Relative humidity shall be maintained at 90 %.

Sample Preparation for Water Vapor Transmission Test ASTM E96

1. Take a test sample with dimensions of 4×4 inches.
2. Take at least 3 samples for one test method.
3. Put Anhydrous Calcium Chloride in the oven at 160 C for 3 hours.

The Procedure of Water Vapor Transmission Test ASTM E96

Take a fabric sample based on the sample cup diameter.

For the desiccant method, first, pour the desiccant (Calcium Chloride) into the sample cup.

1. Mount the fabric sample over the sample cup along with the silicone pad and metallic ring and tighten the screws.
2. Weigh the sample cup and record its weight.
3. Place the sample cup in the WVT tester’s test chamber and start the tester.
4. Depending on the test interval, weigh the assembly every 20 minutes until the test is completed.

For the water method, pour distilled water into a sample cup.

1. Mount the fabric sample over the sample cup along with the silicone pad and metallic ring and tighten the screws.
2. Use a weigh scale to weigh the sample cup assembly and record its weight.
3. Place the sample cup in the WVT tester’s test chamber and start the tester.
4. Depending on the test interval, weigh the assembly every 20 minutes until the test is completed.

Water Vapor Transmission Test ASTM E96 Test Report

1. Make a test report that contains fabric sample characteristics, including thickness, composition, woven, non-woven, or knit.
2. State the testing conditions, including Temperature and relative Humidity.
3. State the method that is followed in the test method. i.e. (Desiccant or Water Method).
4. For the desiccant method, also describe the type of desiccant used.
5. Show the values in g/hr or g/day.
6. State that ASTM E96 is followed for testing.

Experience and Insights on Water Vapor Transmission Test ASTM E96

1. The weight balance should be enough to weigh the combined assembled dish mass. They should also be sensitive to show the mass of any moisture gain or loss.
2. No two sample results can be compared unless both have similar test conditions.

Conclusion

A water vapor permeability test is necessary for determining the water resistance of fabrics. Designers and manufacturers must know how much fabric is breathable and maintain product quality. They can better evaluate and control the moisture transmission qualities of garments and end fabrics if they know the fabric results. It will help them to design more comfortable clothes, which enhances the performance and functional properties of garments.

Similar Test Methods

Other standards are used for measuring the moisture permeability of fabrics. The following list shows these standards.

1. ISO 2528
2. JIS L1099 A and JIS L1099 B
3. BS 7209
4. GB/T 12704

FAQs

1. Which factors affect ASTM E96?

The thickness of the sample is an essential factor while considering results. Thicker materials show lower values. Water vapors need to travel more than thinner material. Fabric made of hydrophilic (water lover) materials also show higher test values than hydrophobic (water-repellent) materials.

2. What is ASTM E96?

The ASTM E96 cup method is a widely used test method that determines how much moisture a fabric can transfer.

3. What is the sample size for Astm E96?

The sample can be taken to the size of a sample cup or a simple 4×4 inch.

4. What is the temperature of Astm E96?

Typically, 38°C is maintained through the test chamber.

Related Resources

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