Why are some fabrics both waterproof and breathable?

The main principle why fabrics are both waterproof and breathable is that water substances in different states have different diameters, which leads to the possibility of their spread.

Water vapor molecules and water droplet diameter

Waterproofness and moisture permeability may seem contradictory on the surface, but they can be consistent based on the fabric structure and processing methods. The diameter of water vapor molecules is generally 4×10-4µm, and the diameter of raindrops is usually more than several hundred microns. Therefore, as long as the diameter of the pores in the fabric is controlled within the range where water vapor molecules can pass but water droplets cannot pass, it can play a waterproof and moisture-permeable role. The fabric’s ability to prevent water penetration depends on the surface energy of the fabric and the contact angle Q of water droplets on the fabric surface. When Q is greater than or equal to 90, the critical surface tension of the fabric is less than the critical surface tension of water, and the fabric can be wetted by water. However, because the fabric has wicking properties (capillary effect) and cannot prevent the penetration of water droplets, appropriate waterproofing is required to make the surface energy of the fabric lower than water. At the same time, due to the cohesion of water, the water droplets become bead-shaped, thus making The fabric is water-resistant.

Further reading:

Waterproof and breathable fabrics mean that water does not penetrate into the fabric under a certain pressure, but the sweat emitted by the human body can be transmitted to the outside world in the form of water vapor through the fabric, thereby preventing sweat from accumulating and condensing between the body surface and the fabric to maintain the clothing’s durability. Comfortable, it is a high-tech, unique functional fabric. The currently widely used approach is to achieve waterproofing and moisture permeability through coating finishing or to achieve waterproofing and moisture permeability through lamination of waterproof and moisture permeable membranes. In addition, gas molecules are generally around 0.3nm, which is much smaller than the diameter of water droplets. Waterproof and breathable fabrics will have certain breathable properties.

Main uses of waterproof and breathable fabrics: racing suits, motorcycle suits, golf suits, waterproof suits, hiking shoes, shower curtains, tablecloths, raincoats, baby bibs, sailing suits, fishing pants, snow jackets, windbreakers, cold-proof jackets, ski suits, Ski gloves, mountaineering clothing, hunting clothing, surfing clothing, horse clothing, assault clothing, combat clothing, lighting accessories, mobile phone waterproof accessories, etc.

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