Originally Posted by AlanG .
Maybe bags would help as long as your socks absorb any additional sweat that may occur. I'd try them over my socks first rather than against the skin. It is pretty easy to test out though.
Originally Posted by alienator .
..... One option that works great is putting a baggie over your each foot before putting your socks on. This stops a lot of evaporative heat loss, but can leave you with a moist foot at the end of a long ride. Saran wrap works well for that, too.
The idea of using a vapour barrier is pretty wide spread among ice/mountain climbers and other people who need to stay outdoors for days on end. Quite a few people also use plastic liners in their sleeping bags for winter camping.
It's not really a case of the barrier making you immediately warmer, there's not a lot of evaporation going on through a thick winter shoe anyhow.
But what is does is to help the outside garments keep their insulating properties. If you're actually sweating, you'll soak the layers closest to the skin fairly fast, ruining the insulating properties(mainly based around their ability to retain air) of those garments.
If you're riding in below freezing, even if you aren't sweating, moisture released from the body will migrate through your clothes until it reaches a point where the moisture will turn into ice, and gradually degrade the insulating properties of the garment as the ice builds up.
It's mainly a boon when it's hard to dry your items between uses, but obviously that depends on how much you're sweating.
I've been using surgical gloves as liners inside my mittens the last winter, and it's worked out real well. Clammy but warm is a definite upgrade from clammy and frozen stiff.