DWR (durable water repellent) is a coating that’s added to fabrics during their manufacturing process to make them hydrophobic, or water-resistant. Most factory-applied DWR treatments are fluoropolymer based, an organic polymer that contains fluorine atoms, like PTFE. Durable water repellents are typically used with breathable, waterproof materials, such as Gore-Tex, and work to prevent the outer layer from becoming overly saturated with water, or “wetting out”, which can significantly reduce the fabrics breathability which will eventually let water through.

As DWR will wear off over time, re-treatment of fabrics is essential to keep them water resistant. Re-treatment products are typically either spray-on or wash-in, and are available from a number of brands including Grangers, Nikwax, McNett, Trek7 and a number of others.

Less common factory methods of DWR treatment involve applying a chemical solution directly to the surface of the material, either by spraying or dipping, using a process called Chemical Vapor Deposition (CVD). CVD is a far more modern form of DWR treatment and has a number of advantages over traditional coating. These advantages are:

  • Use of hazardous solvents and perfluorinated acids are removed from the application process, something that is much more environmentally friendly.
  • Less chemicals are required to complete the process, which is again safer, as well as more cost effective for manufacturers.
  • The outer waterproof layer is much thinner than in traditional application, which works to limit the aesthetic impact this has on the coated fabric, as well as to reduce the overall weight of DWR treated materials

Re-treating DWR Materials

Machine washing DWR coated materials with harsh detergents tends to accelerate the loss of their water resistant coating, making it advisable to wash them with either rain or salt water. Re-treating materials is straight forward, with easy to use and apply treatments being available from numerous brands and retailers in either spray-on or wash-in treatment types. You can also use heat treatment to further protect the material, however this type of treatment is far less accessible to most people, making it more suitable at the time of manufacture than as a home treatment.

Read more about bivvy bag materials or learn which bags we recommend on our best bivvy bags and bivvy bag reviews pages

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