Waterproof fabrics are fabrics that are inherently, or have been treated to become, resistant to penetration by water and wetting. They are usually natural or synthetic fabrics that are laminated to or coated with a waterproofing material such as rubber

Rubber

Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

, polyvinyl chloride

Polyvinyl chloride

Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...

 (PVC), polyurethane

Polyurethane

A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...

 (PU), silicone elastomer, fluoropolymer

Fluoropolymer

A fluoropolymer is a fluorocarbon based polymer with multiple strong carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases.-History:Fluoropolymers were accidentally discovered in 1938 by Dr. Roy J...

s, and wax

Wax

thumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...

. Examples include the rubberised fabric used in Mackintosh

Mackintosh

The Mackintosh or Macintosh is a form of waterproof raincoat, first sold in 1824, made out of rubberised fabric...

 jackets and inflatable boat

Inflatable boat

An inflatable boat is a lightweight boat constructed with its sides and bow made of flexible tubes containing pressurised gas. For smaller boats, the floor and hull beneath it is often flexible. On boats longer than , the floor often consists of three to five rigid plywood or aluminium sheets fixed...

s.

Design

(Alternative spellings include "waterproof breathable" and "waterproof-breathable".)

Waterproof/breathable fabrics resist liquid water passing through, but allow water vapour to pass through. Their ability to block out rain and snow while allowing vapour from sweat to evaporate leads to their use in rainwear, waterproof outdoor sports clothing, tents, and other applications.

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 or Moisture vapor transmission rate

Moisture Vapor Transmission Rate

Moisture vapor transmission rate , also water vapor transmission rate , is a measure of the passage of water vapor through a substance....

  is measured by the rate at which water vapor passes through, in 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 best materials have 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

KPA

KPA may refer to:* Kenya Ports Authority* Kiln phosphoric acid, a dry process to produce phosphoric acid at high temperature in a kiln* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army...

) pressure without leaking (see hydrostatic head

Hydrostatic head

When generating hydropower, the head is a general term used to describe the distance that a given water source has to fall before the point where power is generated. Ultimately the force responsible for hydropower is gravity, so a hydroelectricity plant with a tall/high head can produce more...

).

These values should be taken with some caveats. Rain room tests show that some fabrics with less than 1,000 mm of water resistance keep water out sufficiently for practical purposes. Garments made from these fabrics tested

Condensation

Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 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 through zips, hoods, and seams. Pressure may not be a good measure for rainwear, 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

Breathability

Breathability is the ability of a fabric to allow moisture vapor to be transmitted through the material.-Mechanism:Air Permeability is the ability of a fabric to allow air to pass through it...

 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, rather than membranes, coatings or laminates, can be used to keep the wearer dry. 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 fabrics such as Nikwax Analogy

Nikwax Analogy

Nikwax Analogy is a two-component fabric system for weatherproof clothing based on "biomimicry" of fur .-Technology:...

 or FurTech, 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 thermal insulation, such as those manufactured by FurTech and Paramo

Páramo

The term páramo can refer to a variety of ecosystems. Some ecologists describe the páramo broadly as “all high, tropical, montane vegetation above the continuous timberline”. A more narrow term classifies the páramo according to its regional placement - specifically located in “the northern Andes...

, resist cold bridging

Thermal bridge

A thermal bridge, also called a cold bridge, is a fundamental of heat transfer where a penetration of the insulation layer by a highly conductive or noninsulating material takes place in the separation between the interior and exterior environments of a building assembly .Thermal...

 (heat transferred through layers of poorly-thermal-insulating materials in close contact that would be prevented by a small airspace). When there is cold bridging, vapour on the "dry" side can condense on the cold surface, making it appear that the thin waterproof breathable fabric has leaked.

External links

• "Breathability" comparison of commercial outerwear shell layers, Phil Gibson, 2000, Materials Science
  Materials science
  Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
  
   Team, United States Army Soldier Systems Center