A vapor barrier liner is some type of vapor impermeable layer often utilized and effective while recreating outdoors in very cold conditions. By preventing vapor transfer from your body into clothing, footwear, or a sleeping bag for example one is able to boost warmth and keep insulation dry in conditions where wet insulation would be very difficult to dry and result in compromised warmth. While using a VBL with your clothing and sleeping bag (for sleeping bags, see the Western Mountaineering Hot Sac) is less common and can be effective on longer excursions, VBLs are particularly effective and easy to use for perhaps the most cold-susceptible parts of your body – your feet and hands.

A vapor barrier liner is used to boost warmth and keep insulation dry during cold weather.

My Vapor Barrier Liner / VBL Setup

By utilizing a VBL in these areas combined with waterproof footwear (or for the hands, mittens), one is able to keep boots dry from both the outside and the inside. A common technique for feet, and a similar setup could be substituted for hands, is to use a thin liner sock for comfort, then the VBL itself which can be anything from dedicated, purpose-built items, to bread bags, oven bags, large Ziplocs and anything in between – just something that doesn’t breathe. Over the VBL, your normal winter hiking sock of choice can be utilized. In this example we have a Darn Tough Ultra-Lightweight style sock as a liner, followed by a large size Reynolds oven bag, and finally a heavier Darn Tough cushion sock. However, if you prefer to go a different route RAB also makes their vapor barrier socks as an option.

Easy and ultralight winter backpacking VBL sock setup

In Conclusion

The liner sock and the inside of the VBL will accumulate a minimal amount of moisture before the day is over, but by using the VBL warmth will be increased substantially, and the inside of your boots will remain dry from perspiration. And no one likes waking up to not only cold, but icy frozen boots. A VBL will help on those winter day hikes as well providing a substantial warmth boost when utilized with your cold weather footwear system, as well as when utilized with mittens and liner gloves.

Editor's Note: This article originally appeared in Issue 26 of TrailGroove Magazine. You can read the original article here.