Water repellent and waterproof are totally two different things.

The water-repellent function of a fabric does not equal to waterproof. Many people have a misunderstanding that the water-repellent function of a fabric means it’s waterproof. However, after using it, they find that the fabric will be penetrated after being underwater for a while and it’s not truly waterproof.

Water repellent

In English it’s called water repellent, abbreviated as W/R.

Water repellent refers to the deposition of hydrophobic compounds on the fibre surface, leaving pores on the surface and air and water vapor can still pass through. It generally forms water droplets on the fabric surface (like lotus leaves), so it’s not waterproof but reducing the adsorption of water so that the water can be “repelled” on the surface of the fabric. If the water stays for a long time, it will still penetrate into it.

Water repellent processing uses various chemical materials to attach a layer of ultra-fine ‘needle bed’ on the surface of the fabric, so that the surface tension of the fabric is less than the cohesive force of water. Therefore, when water drops, it forms beads and rolls away instead of spreading and soaking.

Waterproof

Waterproof refers to waterproof and breathable fabrics, which generally refers to the rubber base at the bottom of the fabric, which is divided into coating and lamination.

Coating is generally the extra layer added on the surface.  Lamination refers to a layer of waterproof material. Most waterproof fabrics use laminated (film) materials. There are various treatment methods such as capsule fibre, compact fabric and siliconization etc and they are usually located in the inner layer of the fabric, which is often called “waterproof film”.

Waterproof film is a composite fabric that is made by bonding a thin film with the other fabrics through a pasting process. The fabric itself is not waterproof, so when you wear waterproof clothing in wet weather, you will see water seeping into the clothing, just like clothing made from ordinary fabrics. However, the inner layer of the waterproof clothing is dry and that’s because the waterproof film in the middle of the composite fabric plays a role.

Source: China Textile Leader