Working principle of waterproof and breathable fabrics

In the state of water vapor, the water particles are very small. According to the principle of capillary movement, they can smoothly penetrate into the capillary tube to the other side, thus causing vapor permeability. When water vapor condenses into water droplets, the particles become larger. Due to the surface tension of the water droplets (the water molecules "pull and compete" with each other), the water molecules cannot smoothly break away from the water droplets and penetrate to the other side, which is to prevent Water penetration occurs, making the breathable membrane waterproof.

Types of waterproof and breathable fabrics: There are two main types: water-resistant and water-proof. The former is divided into two types: fiber/cloth type (not windproof but good breathability) and membrane type (windproof but not good breathability). The latter is generally a permeable membrane type, with two or three layers, and is windproof. The two-layer one is softer and more breathable than the three-layer one, while the three-layer one is stronger. Water-resistant or highly-water-repellent fabrics will seep when pressure is applied to them, such as when you sit on a wet stool wearing pants made of this material.

The development of completely waterproof and breathable fabrics began in the late 1970s. The current second generation products are completely waterproof and windproof and maintain good breathability. However, garments made of this kind of fabric are not necessarily completely waterproof, mainly because of water seepage in seams or zippers. To ensure that the garment is completely waterproof, you need to tape all the seams (good garments use waterproof tape). This requires a lot of labor and cost, which is one of the reasons why such clothes are so expensive.