What is Water Vapour Permeability of Fabric?

Water vapour permeability definition: In general, there is a water vapor pressure difference between the front and the back of the fabric, so the water vapor diffuses from the high-pressure air side to the low-pressure air side through the fabric. The water vapour permeable of the fabric refers to the difficulty degree of water vapor passing through the fabric. The water vapour permeability of fabric is an important index to measure the water vapor resistance of clothing.

The Principle of Water Permeability Test

A test specimen is sealed over the open mouth of a test dish which contains water, and the assembly is placed in a controlled environment. Following a period of time to establish equilibrium of the water vapour pressure gradient across the sample, successive readings of the assembled dish are made and the rate of water vapour permeation through the specimen is calculated.

How to Calculate Water Vapor Transmission Rate?

The water vapour permeability index is calculated by expressing the water permeability of textiles as a percentage of the water vapour permeability of a reference fabric which is tested in a water vapor permeability test. After the water permeability test for fabric, the water vapour permeability of the fabric can be obtained according to the water vapor transmission rate unit conversion and the water vapor permeability formula.

Water Vapour Permeability Test Method

The experiment is affected by the test method and the test condition, and the result deviation is large, so it is necessary to select a suitable water vapour permeability test method according to the environment of the products. This instrument is easy to carry and easy to test. It mainly tests the water vapor permeable of fabric in natural environment. In addition, we also have the instrument VIT165B, to test the water vapour permeable of fabric under artificially controlled environment.