DWR stands for Durable Water Repellent and is a liquid based treatment applied to the outer surface of some outdoor gear including both hard-shell and some soft-shell jackets as well as tents.
Its purpose is to provide the first line of defence against the rain in order to prevent the outer fabric of a product from absorbing and becoming saturated with water, oil or grease. It is DWR which gives a piece of outdoor gear that very satisfying run-off when hit with water droplets.
If say a jacket didn’t have a DWR treatment applied to its outer fabric such as the protective nylon on a Gore-Tex jacket, it would quickly absorb the rain where it would sit against the waterproof membrane within and not allow the jacket to breathe so well in the way that Gore jackets are so well-known. This is called “wetting out” and despite water not being allowed to pass through the waterproof membrane, it can leave the wearer feeling clammy and damp within as the breathability of the jacket has been compromised.
After a fair amount of rain or a machine wash, a jacket’s DWR treatment will wash out and so for optimal performance and breathability, it is vital to reproof your jacket with either a wash-in or spray-on solution such as TX Direct from Nikwax or Performance Clothing Repel from Grangers. These solutions are easy to reapply and will ensure that your jacket’s water repellency is back up to high-performance standard allowing you to properly enjoy your time out on the hill without fear of wetting out and feeling clammy.