The biggest dirty little secret in the outdoor industry is that rain gear won’t keep you dry. It doesn’t matter if you buy a high-end $450 Arcteryx Gore-tex Parka or wear your bathrobe, they’ll both Wet Out in continuous rain and leave you soaking wet.
This happened to me (for the millionth time) in heavy rain over the weekend on a I was co-leading for the Appalachian Mountain Club. We ended up walking out because the rain was so extreme and many of our participants were already soaked to the bone. I was nearing my limit as well because my rain jacket, rain pants, mid-layers and base layers had wetted out, and the pace of the group was slow enough that I couldn’t generate enough body heat by walking fast to stay ahead of the chill (see Why You Should Hike in the Rain.)
What is Wet Out?
Wet Out occurs when your rain gear stops venting perspiration because the humidity outside your jacket is higher than on the inside. During sustained rain or drizzle, your perspiration accumulates on the inside side of the your rain garments and will gradually soak your inner layers. It doesn’t matter if your rain gear is made out of Gore-tex, eVent, Tyvek, Nylon or some other breathable membrane, all rain gear will wet out, sooner or later.
What about DWR Coatings?
Most 2-3 layer breathable rain jackets and pants are coated with a Durable Water Repellent (DWR) finish that makes water bead up and roll off them without saturating the exterior fabric. The breathable layer is often sandwiched under or between two fabrics which protect it or provide a secondary surface that moisture can evaporate from. When the DWR coating wears off, the external fabric can become saturated and prevent the internal membrane from passing water vapor, even if it is not raining anymore, because the humidity on the outside of the middle layer is still at 100%.
This is a good reason to keep maintain your DWR layer regularly by washing your rain garments and reapplying a DWR conditioner like Nikwax TX-Direct Spray-on Water Repellent Treatment to restore it, but it doesn’t change the fact that perspiration accumulation inside the breathable layer will wet out your garments when it is raining outside.
Wet Out Mitigation Strategies
If your rain gear starts to wet out, you run the risk of getting chilled or even hypothermic in cooler weather conditions. Here are a couple of things you can do to mitigate this risk and still keep hiking.
- Hike faster, keep eating and drinking to keep you core temperature up. Dehydration can accelerate the onset of hypothermia, so keep drinking even if you don’t feel thirsty.
- Put on additional base and mid-layers. While these may eventually become saturated, additional layers will help you retain more body heat. They will also disrupt the transfer of cold from the surface of your jacket or pants to your skin. Your layering system should work to keep the layer against your skin dry and move moisture away from your skin.
- If you have pit zips on your jacket, open them to help vent moisture. Pit zips are underrated in this era of breathable, waterproof garments.
- If you can’t stay warm, set up a shelter and get into your sleeping bag to warm up. It will stop raining eventually.