Waterproof and breathable fabric waterproofing principle

Principles of waterproofing of waterproof and breathable fabrics

The waterproofness of fabrics refers to the fabric’s barrier resistance to the penetration of liquid water. Traditionally, the term “waterproof fabric” is used to describe a fabric that is completely impermeable to water under the application of water pressure, whether it is liquid water or gaseous water, and does not cover the entire service life. This feature has always been maintained. Water cannot pass through the fabric, but it can wet the surface of the fabric. Usually, the fabric can be made waterproof as long as the surface of the fabric is coated or the fabric is compounded with a dense film that cannot pass water.
Water repellent fabric refers to the fabric’s ability to resist the penetration of water under static conditions without being subjected to any external force. Water-repellent fabric allows gaseous water to pass through, but does not allow liquid water to penetrate under static conditions. Its essence is that it does not allow water to wet the fabric. This requires the fabric to have low surface energy.
Waterproof and Moisture Permeable fabric refers to the fabric’s ability to be completely impermeable under the application of water pressure, yet permeable to water vapor in daily use, and to maintain this characteristic throughout the entire period of use. The essence is that there is a huge difference between the volume of water vapor molecules and water droplets. In order to improve the waterproofness, it is usually required that the outer surface of the fabric is not easily wetted. The American Association of Textile Chemists and Colorists (AATCC) and the American Society for Testing and Materials (ASTM) define repellency as the ability of a fabric to resist penetration or both.
There are two ways for liquid water to enter the inside of clothing through the fabric of clothing:
1. After external water, such as rain or snow, contacts the fabric, the fabric is moistened. Through the capillary effect, the water is transported to the inside of the fabric and other parts of the fabric surface through various gaps and holes in the fabric. This situation is mainly related to the surface energy of the fabric. It is related to surface roughness and appears as a spontaneous process.
2. Under a certain external pressure or its own kinetic energy, water directly penetrates the gaps and holes in the fabric and enters the inside of the fabric. In addition to being related to surface energy and surface roughness, this situation depends to a large extent on the larger gaps in the fabric. The size of the hole. Therefore, the waterproofing of fabrics must also include preventing the fabric from being wetted by water and preventing liquid water from penetrating and penetrating.

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