Durable Water Repellent, or DWR for short, is a spray or wash-in treatment applied to the outside of outdoor clothing and gear to make them more resistant to water.
It’s an important part in the construction of waterproof clothing, but it’s not what makes them waterproof. The waterproofness comes from the membrane laminated between the outer fabric and the inner lining. The DWR coating prevents the outer fabric from becoming saturated with water. When the outer fabric is wet it reduces the breathability of the membrane, making you feel damp and clammy, especially if you are warm and sweaty.
Sometimes it can feel like your waterproof clothes have leaked through, but it’s just the outer fabric that is soaked and moisture from your own body that is trapped on the inside of your clothes. The DWR treatment does not make your clothes more waterproof, but it helps them perform better in other areas, which makes them more comfortable to wear and improves the experience.
The DWR coating is a chemical treatment that makes the outside of the fabric hydrophobic. It does this by building a film on the outer fabric, which reduces the surface tension of the fabric. This creates a higher contact angle between the outer fabric and the water in contact with it, making the water bead up and become rounder and thus easier to repel.
The film can wear off completely over time or compromised by dirt and oils from your body. When this happens, the contact angle between the outer fabric and the water is lower and the surface tension of the fabric increases. The water will no longer repel perfectly, instead it will spread out, cling to the surface of the fabric and eventually seep into it.
The DWR coating wears off over time through heavy use and several washings. To keep your gear performing optimally, you need to reactivate or reapply the DWR treatment.
But how do you know if your DWR is working? You can easily test the DWR coating on your gear by filling a spray bottle with water and spraying it on your gear. If the water beads up on the surface of the fabric and easily fall off when you shake the garment – your DWR is working properly. If the water soaks into the outer fabric and makes it darker – your DWR is not working as it should and you need to reactivate it or reapply.
Every time you wash clothing that has a DWR treatment you need to reactivate it with heat. You can easily do that by throwing your clothes in the dryer for 20-30 minutes or by ironing them on low heat without steam and with a towel between the iron and the fabric. In our guide on washing waterproof clothing, you can learn more about how to reactivate the DWR.
If washing and reactivation were not enough, the DWR treatment on your gear has worn off and needs to be reapplied. You might need to do this every 3-6 months depending on how much you use your gear. In our guide on how to waterproof your clothes and gear you can read more about how to re-apply the DWR with a spray-on treatment.