Waterproof textile which breaths may be defined as intelligent waterproof fabric, which is permeable to water vapour i.e. perspiration at a rate of 2000-2500 g/m2/day for light applications and 4000-5000 g/m2/day for heavy applications. By 1998 it was common to see claims of 10000 g/m2/day.
Waterproof fabric completely prevents the penetration and absorption of liquid water in, in contrast to water-repellent fabric, which only delays the penetration of water. Traditionally, fabric was made waterproof by coating it with a continuous layer of impervious flexible material. The first coating materials used were animal fat, wax and hardened vegetable oils. Nowadays synthetic polymers such as polyvinylchloride (PVC) and polyurethane are used. Conventional polymers coatings are considered to be more uncomfortable to wear than water-repellent fabric, as they are relatively stiff and do not allow the escape of perspiration vapour. Consequently they are now used for emergency rainwear. Water-repellent fabric is more comfortable to wear but its water-resistant properties are short lived.