Cold feet suck. Proper choice of boot is critical, but some people just can't keep their feet warm even with Antarctic-class boots on. ThermaCELL heated insoles are designed to provide rechargeable, wirelessly controlled heat right where you want it.
The Thermacells replace your normal insoles with a comfortable footbed that comes in five sizes from small to XXL. Although the small says it will go down to size 4.5 that seems a little optimistic. Even thought the front can be trimmed back about half an inch, maybe 5.5 is more reasonable.
Once installed there are two heat levels available, medium (100F) and high (110F), as well as an off setting to conserve battery life. The lithium ion batteries can last up to five hours, but that would be under optimal conditions with the intelligent heat regulation working away.
The best use for the ThermaCELLS is where you're on your feet and thus putting pressue on the heated insoles. You don't want to run them so hot that your feet start sweating, so experiment with different heat settings and also with different weight socks. It may be that a thinner sock will work better by letting the heat from the insoles through to your foot. Remember, you're not trying to bake your feet, just keep them from getting uncomfortably cold. If you've got cold feet and your socks, boots and chemical warmers aren't doing the trick, ThermaCELL heated insoles may become your best friend.