Liquid proof, vapour permeable fabrics

Physiological problems arise if water resistant clothing does not allow the free passage of perspiration vapour. The consequence for active wearers is the progressive dampening of underclothing. In mild cases discomfort is caused, but in severe conditions injury, incapacitation or death by hypothermia or hyperthermia may be the result.

The consequences may be simply discomfort if a moderate level of activity is undertaken in a cold, wet climate but high levels of activity in hot, moist climates may lead to hyperthermia and low levels of activity following high activity may lead to hypothermia because of the cooling effect of sweat wetted waterproof clothing.

One of the biggest growth areas in coated fabrics is that of waterproof/vapour permeable materials, commonly called waterproof/breathable fabrics. There are four main types of 'breathable" fabric:

1. High-density woven fabrics
2. Microporous coatings and films (poromerics)
3. Hydrophilic coatings and films
4. Combined microporous/hydrophilic layers, e.g. Gore-Tex., have a thin outer layer of hydrophilic material on a microporous film. The hydrophilic layer is intended to protect the surface of the microporous film against blockage and contamination