Some mountain climbers use vapor-barrier socks to keep double-layered boots dry. These boots have a warm removable inner liner and a plastic outer shell. The plaster outer shell keeps out moisture, but because the boots don’t breathe, perspiration soaks the socks and liner which can then freeze. Vapor barrier (VP) sock are used to prevent this problem. The VP socks hold in the moisture to keep the boot dry.
I’ve never needed this, but I found a new use for the barrier socks. I don’t wear mountain climbing boots or double-layer boots when snowshoeing or hiking in the snow. If I know I’ll need crampons, I do take heavier and stiffer winter boots, the Lowas Tibet GTX, which are reasonably waterproof, but it is not a mountain climbing boot. For most trips, I wear lighter and more breathable hiking boots, the Asolo Fugitive GTX. The Asolo are fine with snowshoes but too flexible for crampons (there is a risk of the crampons coming off). The Asolo boots are not fully waterproof nor long-lasting. The seams tend to break in spots creating holes for water to enter and the boots get soaked in the shoulder seasons. Despite these flaws, they are comfortable and one of the few wide-width shoes available.
The usual solution for wet boots is to change out of wet socks at camp, putting on a new liner sock and thicker outer sock, and setting the wet socks and boots aside for the evening. This way my feet are dry and warm at camp. But here’s the problem. What if I need to put my wet boots back on around camp? To avoid getting my fresh socks wet or having to put the wet socks back on, I would slip on a plastic bag on each foot. Then I could put the wet boots back on without getting my socks wet. This is a fine solution, but VP socks can do the same job while only adding about 2 ounces to my pack weight.
Adding any needless weight to my pack is something I want to avoid. However, you can walk around camp in VP socks and they don’t fall off as plastic bags do. That is, most of the time, I don’t need my boots to walk around camp. The VP socks do the job. VP socks are lighter and more compact than down booties. The VP socks do add some warmth too. I still regard them as luxury items, but worth taking on shoulder season trips when I don’t want booties. I think of VP socks as booties without the insulation or shoulder-season camp booties. They are intended for one purpose in extreme cold weather, but actually work for another purpose in mild shoulder-season weather.