Hand warmers are awesome kit for cold climates... Unless I've fallen for some sales hype. <img src="/images/graemlins/laugh.gif" alt="" />

Someone who's more medically inclined might be able to put this better than I, but from my understanding:

When your body temperature drops, the blood vessels in the outer regions of your body constrict both to reduce heat loss, and to keep the circulation inward where vital organs are. Err... Perhaps that is the same thing explained differently. LOL In any case, the effect on your extremities from this is a loss of sensation, reduced functionality, and possibly frostbite depending on the temperature.

Hand warmers will help maintain finger functionality and help prevent frostbite. Dexterity might be what it takes to get a fire started in an extreme survival siutation especially when you find you have to take off your gloves for a period of time.

You have to be careful though, some hand warmers run in excess if 130?F.