Reynolds Oven Bags! work great as vapor barrier liners for your winter boots because they’re super durable, and relatively inexpensive.

Vapor Barrier Clothing

If you’re not familiar with Vapor Barrier clothing, you haven’t been reading Section Hiker long enough. I’ve been messing around with the idea for years after being introduced to it by my friend Chris. I read more about it in Mark Twight’s awesome book, Climbing Light and Fast and have been incorporating vapor barrier components into my winter clothing systems ever since (vapor barrier liners are actually the thing that first got me interested in ultralight backpacking.)

The basic principle is this:

Wrap yourself in an impermeable membrane like plastic and raise the relative humidity of your skin (by sweating a little bit) so your body thinks it’s on a warm tropical beach and not on top of a freezing cold mountain. Your body will stop sweating because the relative humidity next to your skin has increased, which means you’ll need to drink less water to stay hydrated. The plastic barrier also prevents the transmission of moisture into your higher layers and you’ll be able to wear less insulation because your sweat isn’t degrading its ability to trap your body heat.

Anti-breathability

Vapor barrier clothing flies in the face of everything you’ve ever been told about breathable clothing, especially the part where breathability helps preserve the insulating properties of your warmer layers. This is particularly helpful on multi-day trips where you want your insulation to remain consistently effective for the duration, so that you don’t need to bring extra dry clothing or stop to dry your gear off in the sun.

Vapor barrier clothing and liners work best in very cold temperatures, starting at about 10 degrees fahrenheit or less. Much warmer than that and you’ll sweat too much, which gets uncomfortable. They also make you much more aware of your perspiration rate and you’ll want to dial down your activity level if you find yourself overheating.

My Cold Weather Boot System

When I go on winter backpacking trips, I wear a mountaineering boot that has a removable insulating liner so that I can sleep with it in my sleeping bag to prevent it from freezing solid. However, you don’t have to do this (sleep with them or wear a removable boot liner) if you wear a vapor barrier sock because it prevents the passage of sweat from your socks to the boot. They also help keep your feet and boots much warmer in camp when you’re sitting around melting snow for drinking water because your socks and boots remain dry.

When I hike in my mountaineering boots with a vapor barrier liner, this is the layering scheme I use. I often wear boots with a removable liner in very cold weather because I find them comfortable, but I also sometimes I wear unlined mountaineering boots. It depends on the demands of the trip, trip duration and weather conditions. This system will work either way.

I wear a very thin polyester sock as a base layer over my foot. These socks absorb very little moisture and I wear them for comfort, so I don’t have plastic touching my skin. The next layer out is a large-size Reynold’s Oven Bag (see above). I pull an REI wool expedition sock over that as an outer sock for warmth and cushioning. Next is my removable boot liner. Both it and the wool expedition sock stay completely dry when I wear a plastic oven bag underneath them. The outer waterproof mountaineering boot.

Using a vapor liner works best if it’s 10 degrees fahrenheit or colder. The colder, the better. Just make sure you get the large sized Reynolds Oven Bags and not the Turkey-Sized ones. Those are too big, even if they do have multiple uses.

Disclosure: The author purchased a pack of five large size Reynolds Oven Bags from Reynolds Consumer Products with his own funds.

Updated 2016.

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