Does it seem like your high-performance rainwear is giving you a damp, clammy feeling you didn't used to get when you bought it new? Don't despair -- and don't just run out and buy another jacket just for this reason. The problem is likely a simple one: You probably just need to renew the DWR and you'll get a lot more life out of your garment.
What is DWR? Virtually all rainwear is treated with a DWR, or durable water repellent finish. While a waterproof/breathable membrane will stop water from penetrating a rain jacket's interior, the DWR prevents precipitation from saturating the jacket's exterior. When the DWR breaks down, the rain jacket's exterior becomes waterlogged and heavy; the damp fabric tends to sag and cling to your skin, which gives you that wet, clammy feeling.
What many people fail to realize, is that DWRs diminish in performance due to a number of factors—dirt, body oils, abrasion and repeated launderings. Fortunately, a jacket's performance can usually be revived either with a proper cleaning, or by reapplying the DWR with a spray-on or wash-in product, an easy process you can do at home.
How to Test the DWR?
Test your rainwear by sprinkling or spraying some drops of water on its exterior. Does it bead up and roll off? Your DWR is in good shape. If you give the fabric a single strong shake, does most of the moisture fly off? Ditto.
If, however, the water sits on the fabric and that section begins to darken slightly, water is making its way to the fibers and wetting the fabric. It's time to revive your DWR.
Good news: DWR coating does not impair your jacket's breathability. Rather than coating a textile's entire surface, DWR coats individual fibers, leaving the space between the fibers open for breathability.
How to Revive a Rain Jacket's Water Repellency?
First step: cleaning. Washing away dirt and oils does much to restore a DWR's water-shedding abilities. Follow the cleaning instructions for the type of rainwear you own. You can usually find instructions on the label or by looking it up on the manufacturer's website.
Next step: Apply heat. After washing, exposure to heat does the most to bring a DWR back to life. Generally speaking, you should place the garment in a dryer set for low or medium heat for up to 15 minutes to reactivate the DWR finish. Follow the manufacturer's recommendations on whether or not to use a steam iron.
How to Apply New DWR?
If the steps above—cleaning and heating—aren't enough to revive your DWR (i.e., rain still soaks into the exterior fabric of your jacket), it's time to reapply a new DWR coating.
This step eventually becomes necessary due to excessive abrasion from rocks, repeated contact with hipbelts and shoulder straps or simply years of multiple launderings. A DWR can be reapplied (perpetually, in fact) via a spray-on or wash-in DWR revival product. Simply follow the manufacturer's instructions for the type of DWR product you choose.
How DWRs Work?
DWRs work by increasing the "contact angle" or "surface tension" created when water contacts a textile. Basically, a high contact angle creates a microscopically "spiky" surface that suspends water droplets on the outer fringe of the fabric.
An optimized DWR keeps droplets in a rounder shape—like a dome-shaped bead. The rounder the droplet, the easier it rolls off the fabric. A low contact angle permits droplets to assume a flatter shape, one that can spread out like a splotch, cling to the fabric's surface and eventually seep into it.
View more details about DWR fabric.