Durable water repellent
DWR (durable water repellent) is a coating added to fabrics at the factory to make them water-resistant (or hydrophobic). Most factory-applied treatments are fluoropolymer based. Durable water repellents are commonly used in conjunction with waterproof breathable fabrics such as Gore-Tex to prevent the outer layer of fabric from becoming saturated with water. This saturation, called 'wetting out,' can reduce the garment's breathability (moisture transport through the breathable membrane) and let water through. As the DWR wears off over time, re-treatment is recommended when necessary. Many spray-on and wash-in products for treatment of non-waterproof garments and re-treatment of proofed garments losing their water-repellency are available from sources of sporting apparel. Sprays are made by Grangers, Nikwax, McNett, Trek7, and others.
Older methods for factory application of DWR treatments involve applying a solution of a chemical onto the surface of the fabric by spraying or dipping. More recently the chemistry is applied in the vapor phase using Chemical Vapor Deposition (CVD) machinery. The advantages of CVD include: (1) It eliminates the use of hazardous and environmentally harmful solvents in the application process; (2) The process requires less chemical; (3) the waterproof layer is extremely thin and has less effect on the natural look and feel of the fabric. Later advances have eliminated perfluorinated acids, considered to be potentially hazardous to human health by the US Environmental Protection Agency, from the application process.
Certain types of fabrics need to be re-treated to maintain water-repellency. Washing the garment with harsh detergents usually accelerates DWR loss. Just rain water or salt water doesn't affect DWRs. Affected garments can be treated with a 'spray-on' or 'wash-in' treatment to improve water-repellency. Heat treatment reactivates the factory applied repellent finish and aids the repelling of water, and other liquids such as oils.
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