If you’re used to thinking about layering in winter, forget what you know, because vapor barrier clothing helps you stay warm and dry in a radically different way than conventional layering approaches.
Vapor barrier clothing is not breathable and is normally worn next to the skin or over a thin wicking layer. It’s designed to prevent perspiration from wicking up through your layering system, so it’s good on multi-day trips when it is very cold and you have a limited ability to dry wet clothing. It also helps reduce the amount you sweat by fooling your skin into “thinking” that it’s already in a warm and wet micro-environment where further perspiration is unnecessary. It’s very counter-intuitive, but it works surprisingly well.
The most common applications of vapor barrier clothing are in boots and winter sleeping bags, where perspiration can significantly degrade the insulation value of down or synthetic fill, particularly in cold temperatures on multi-day trips. Sleeping bag maker, Western Mountaineering, makes a vapor barrier liner called the HotSac VBL, which is used for this purpose. I used to own one and found it a bit uncomfortable, but some people swear by them.
Vapor Barrier Socks
I started wearing vapor barrier socks this winter as an experiment to see if they’d help keep my mountaineering boot liners dry on day hikes and winter backpacking trips. Although I like my Scarpa Omega double plastic boots a lot, I’ve been thinking about buying a second, lighter weight pair of mountaineering boots without a removable liner that have a little more ankle flex and fit better than a plastic boot. I’m hesitant to wear a boot like this though for overnights or cold weather trips however, because I know that I’ll soak them with perspiration; hence the desire to try a vapor barrier sock system that can keep them dry for multi-day trips.
For my winter boot system (see photo above), I’m using a pair of Rab Vapor Barrier Socks made of silnylon, which are seam taped to prevent moisture from leaking out. I wear them over a very slippery black nylon dress sock (gold toes) and then cover them with an expedition wool sock from REI. Next my foot goes into the heat molded foam Intution liner that came with my mountaineering boots and then into my plastic Scarpa Omegas. After the boot is on, I put on a set of Hillsound gaiters over my ankles and calves to keep snow from wetting my socks and to provide insulation for my calves.
Before I used vapor barrier socks, I’d completely soak out the liner socks, wool socks, and Intuition liners with perspiration on winter day hikes. On multi-day backpacking trips, that meant sleeping with my liners in my sleeping bag at night to keep them from freezing and to dry them out. As you can imagine, this is a somewhat unpleasant thing to do, even in a big -25 degree down sleeping bag.
But after I added vapor barrier socks to my boot layering system, the outside of the vapor barrier sock, the wool sock and the foam Intuition liner come out of my boots bone dry at the end of a hike. It’s a pretty remarkable difference. So far, I’ve done a dozen major winter hikes using these Rab VB socks, with temperatures ranging from 10 below zero to about 20 degrees Fahrenheit, and I’m hooked. It’s really convenient not to have to worry so much about drying my socks and liners after a hike or on an overnight.
Rab Vapor Barrier Socks
There’s nothing fancy about the Rab Vapor Barrier socks I’m using. They’re just made of silnylon and seam taped to prevent moisture from escaping. They have a piece of elastic sewn in that holds the fabric flush with your leg at the shin and an additional piece of shock cord a bit higher up. Some people I know use bread bags to achieve the same effect, but I like the robustness of the VB socks, so far.
How does my foot feel inside the vapor barrier sock? It doesn’t feel wet. If anything, it feels like I’m wearing a sock that’s slightly too big over the black dress socks I use for my liner layer, but it’s not that annoying, and I quickly forget about it once I start hiking.
When I strip down after a hike, the black dress liner sock comes out of my boot slightly damp, but not soaking wet as one might expect. This has convinced me that my foot is really sweating less overall, because the inside of the vapor barrier sock is so humid.
Moreover, when I pull the damp liner off my foot, the skin is not wrinkled and prune-like, but looks absolutely normal. Nor do my feet smell terribly bad, but the vapor barriers liners do pick up an unpleasant odor after a few days if not washed or rinsed out between hikes.
Warmth-wise, I haven’t really noticed any difference between wearing a vapor barrier sock and hiking without one. That’s not that surprising since my mountaineering boots are rated for -30 degree temperatures and I haven’t been in that kind of weather this year.
Even though I’ve owned these Rab Vapor Barrier socks for a few years, this was really the first winter that I’ve started using them on a consistent basis. Honestly, they work great and I plan to continue wearing them this winter for all of my hikes and overnight trips.
If you’re interested in learning more about vapor barrier clothing and lightweight gear for mountaineering, one of the best sources I’ve read is Mark Twight’s Extreme Alpinism: Climbing Light, Fast, and High.
Written 2012. Updated 2018.Editor's note: Help support this site by making your next gear purchase through one of the links above. Click a link, buy what you need, and the seller will contribute a portion of the purchase price to support SectionHiker's unsponsored gear reviews, articles, and hiking guides.
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