What are the factors that affect the water permeability (water resistance) of fabrics

The water permeability of a fabric is the ability of liquid water to penetrate from one side of the fabric to the other. Generally speaking, there are three main factors for the waterproof and water permeability of fabrics:

1. The wettability of fiber surface

When the fiber contact angle θ<90°, the fiber assembly material is a water-conducting material, and the tight structure will only cause more capillary pores to wick and conduct water. When the fiber θ>90°, the fiber has water-repellent characteristics, and the tighter the fabric structure (that is, the smaller the pores), the better the water-repellent effect. Therefore, it is better to discuss the waterproof or water permeability of the fabric only when the contact angle of the fiber is known.

2. Fabric coating

A continuous film layer that is impermeable and insoluble in water is coated on the surface of the fabric to reduce the water permeability of the fabric and the fabric is therefore impermeable. It is not very suitable for clothing, but can be used for tarpaulins or ponchos. If a waterproof, microporous coating film is used, a coated fabric with excellent waterproofness, water permeability and air permeability can be formed.

3. Environment

Water-repellent fabrics or coated fabrics are mostly made of non-hygroscopic fibers or coated materials, so changes in relative humidity will not affect their waterproof performance. The water-conducting fabrics are mostly hygroscopic fiber materials. The relative humidity increases, the moisture absorption of the fiber is enhanced, the fiber swells and the capillary action is enhanced, so the water conductivity of the fabric is enhanced. The effect of temperature is the same as humidity. Therefore, the environment has a great influence on the water conducting fabric.