 
Waterproof fabrics are usually natural or synthetic fabrics that are laminated to or coated in some sort of relatively waterproofing material, such as rubber, polyvinyl chloride (PVC), polyurethane (PU), silicone elastomer, and wax. Examples include the rubberised fabric used in Mackintosh jackets and inflatable boats.
(Alternative spellings include "waterproof breathable" and "waterproof-breathable".)
Waterproof/breathable fabrics resist water droplets from passing through while at the same time allowing water vapour through. Their ability to block out rain and snow while allowing vapour from sweat to evaporate lends to their use in outdoor sports clothing and single wall tents.
Standard laboratory testing protocols define the performance of these fabrics. Water resistance is measured by the amount of water, in mm, which can be suspended above the fabric before water seeps through. Breathability is measured by the rate at which water vapor passes through, in the units of grams of water vapour per square meter of fabric per 24 hour period (g/m2/d), often abbreviated to just "g". In recent years, some, but not all sporting goods manufacturers have begun including this information on their product labels. Typical mid-range fabrics tend to have values of 5,000 mm of water resistance and 5,000 g of breathability; the highest end materials boast 20,000 mm and 20,000 g.
One specific definition of "waterproof/breathable" requires the fabric to withstand over 1,000 millimetres of water (9.8 kPa) pressure without leaking (see hydrostatic head)[citation needed].
These values should be taken with some caveats. Rain room tests show that certain fabrics with less than 1,000 mm of water resistance can still keep you dry. Such garments tested in the Leeds University Rain Room show no signs of leakage after 4 hours of heavy simulated rain, 5 times heavy British rain. However, some garments made from fabrics that exceed 20 000 mm have leaked due to the design of zips, hoods, and seams. Pressure may not be a good measure for rain wear, as the force of the rain drop on the fabric also depends on how much the fabric moves. However, pressure is a good measure for sitting on wet ground or similar situations. In addition, the breathability of nearly all waterproof/breathable fabrics is very dependent upon weather conditions, especially temperature and humidity.
Fabric construction which directs water away from the body can be used to keep the wearer dry, rather than membranes, coatings or laminates. This means that perspiration can be moved away from the body more effectively as both liquid water and water vapour can be directed. These are Directional like Nikwax Analogy or FurTech fabrics, which are also breathable in the conventional sense (although these examples are actually a combination of two different fabrics, a directional "pump" layer underneath a distinct windproof and water resistant outer layer, and while effectively completely waterproof against rain they would fail a strict hydrostatic head test as given in the definition above).
Fabrics can also be water proofed by a spray (this might alter the quality of the fabric).
Garments that combine waterproofing with some insulation, such as those manufactured by FurTech and Paramo, resist cold bridging. This is a term used by civil engineers to explain how poorly insulated walls can suffer from condensation on the inside. Cold bridging is a considerable problem in thin waterproof breathable fabrics and can lead wearers to surmise that the fabric has leaked.
|
