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 the fiber surface

When the fiber contact angle θ<90°, the fiber aggregate material is a water-conducting material, and the tight structure will only lead to more capillary wicking and water-conducting. When the fiber θ>90°, the fiber has waterproof characteristics, and when the fabric structure is tighter (that is, the pores are smaller), the waterproof effect is better. Therefore, only when the contact angle of the fiber is known, it is better to discuss its waterproofor water permeability.

2. Fabric coating

Coating the surface of the fabric with a continuous film layer that is impermeable and insoluble in water reduces the water permeability of the fabric and the fabric is therefore not breathable. It's not very suitable for clothing, but it can be used for things like tarpaulins or rain ponchos. If a waterproof and microporous coating film is used, it can form a coated fabric with excellent water resistance, water permeability and air permeability.

3. Environment

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