moose42 wrote:When camping in the cold tossing a hand-warmer by your feet and another one by your chest area 30-60 minutes before going to bed will make sleeping even in a -30 bag much nicer.
When I was running an outdoors program for a local university several years ago (okay, more than a decade), I ALWAYS packed extra heat pads for those students/participants who either didn't have proper camping gear or forgot to pack correctly for the high desert (where the nights can get below freezing even if the days are t-shirt weather). For these poor souls, I always had plenty of those 12-24 hour charcoal-activated heat packs and I'd tell them to put one in the foot of their sleeping bag at least an hour prior to their heading off to bed (and get the extra air out of the foot of their bag by using extra clothing, etc. - dead air is harder to heat)
I don't remember how many students I saved from shivering their butts off during the night and not getting any sleep because they brought out those old flannel slumber-party sleeping bags for use in near freezing temperatures. We encouraged them to rent proper bags from the outdoor rentals, but being typical college students, they preferred to
not listen to people with more knowledge & experience, even those trying to make their trip more comfortable and restful. I have to admit that the women were far more accepting of the suggestions than the guys, especially the jocks who thought they could tough it out - 'cause they've played some sports and been through football "hell-week" (college football "hell-week" is NOTHING compared to the SEAL's "HELL-WEEK").
When I went through SCUBA training, they taught us that the vast majority of heat loss comes from where the skin in the thinnest, and that's the HEAD, HANDS, & FEET. You keep those warm, and the rest of the body will follow. Shoving students into foot-heated sleeping bags, and with watch-caps on their heads always made for warm students who usually slept very well after I exhausted them during the day.
I've used electric socks, and find them useful for the times I've needed them. Unfortunately, there's no way to control the amount of heat coming across your toes. It's either an ON or OFF situation, but it's pretty easy to access the snap containing the contact for the battery on each foot/heated sock (usually a single "D" cell battery on each sock). I found them quite handy for when you need to stand watch on cold concrete slabs while either guarding prisoners or on the flightline guarding aircraft.
The socks themselves are usually wool socks with (maybe) some cotton woven in to help spread the heat, but the wool isn't affected by either wetness or sweat. Considering the cost involved, I felt they were a good present and the recipient agreed (who works in a local jail walking on cold concrete ALL DAY LONG - and NOTHING like standing in formation for 20 minutes, the jail is MUCH WORSE for having the cold seep through your boots).
Bottom line, YMMV and each person will have to make their own decisions and choices, using whatever information is available to them at that time.
*IF* someone you know is considering getting such an item, please have them check the return policy in case they fall under the non-refundable electronics instead of the usual clothing policy.
I still have and occasionally USE my battery-heated socks, and AFAIC, they still come in DAMN handy!! I like them enough to give them as gifts to those working in environments where they may be standing on cold concrete for hours at a time - so the cold seeps up into the feet and soles, causing the body to cool and perhaps get cold.
HEAT the HEAD - the HANDS - & FEET, and the rest of the body WILL follow.