hand warmers in sleeping bag

Very small thermal mass => very little heat energy +. very short life and very small area warmed.

You would be better off using the weight allowance for a better bag or better clothing.

Cheers

Thanks for starting this thread. cool product!

You will enjoy this:
http://www.backpackgeartest.org/reviews/Clothing/Accessories/EZ%20Heat%20Reusable%20Hand%20Warmer/Owner%20Review%20by%20Adam%20Bowerman/

When I go testing the limits of my gear I take most of the time a handwarmer, usually a white gas handwarmer or a single use heater.
When putting it at 3 a.m. on the solar plexus it is a wonder how fast you will feel warm and comfortable again.
The white gas handwarmer is really hot, but no open flame, for 14 hours.
Even in a good sleeping bag I am not always capable to stay in a relaxing warm vs. just warm enough. A bit external warmth can make a big difference for me.

Before you get into your sleeping bag, it helps if your heart rate is up. This pumps blood to your extremities and will warm you up very quickly. If you are able, try walking briskly or do jumping jacks, before climbing into your tent. If it's raining I just do sit-ups before "zipping" in. An old guy I met in the late 60's taught me this trick. It really works. If I wake up, cold, in the middle of the night, I just do some vigorous moves and get my pulse pounding.

Justin:

I've brought these into my bag just to warm some cold spots. I liked having them. I've held them in my hand or put them on my groin when I woke up a little on the cold side. What you do not want to do is put them under your clothing on your skin or fall asleep with them beneath you – I fell asleep once and it was between my neck and the bag and I had a nice red mark for about 24 hours – it woke me right quick….

Hmmm. This forum has given me an idea for sewing a pocket into a camp pillow or something fitted with a velcro closure that's big enough for a hand warmer. This way, it's not directly touching your skin but would hopefully still keep your pillow warm. Anyone think it would work? Probably worth a shot…

I often have bricks of ice for feet/hands so I use the single use warmers a LOT in winter.

I even use the insole ones for my boots if I will be hiking in temps under 10*.

Often on chilly nights I will crack two and put them down under my feet inside my bag to warm me up. Helps me warm up right away.

As for changing my clothes instead….that doesn't work. In winter I often wear down socks over wool socks. Heck, I wear winter wear at home and am still cold :-P

So yes, they can help.

I honestly have always filled a Nalgene bottle (alas the BPA) with boiled water, tossed it into the sleeping bag before bed, and it keeps me warm on those cold nights. Cheap, multiuse (okay, you got to use the safe Nalgene bottle now) but effective. If the bottle is too hot, just wrap the bottle in a sock.

The coldest I've ever been was last spring on a canoe trip, and I doubt if it got down anywhere close to freezing. I had put a handwarmer in the foot of my sleeping bag, and I've often wondered if that had something to do with it. Maybe it was just the high humidity, but I had to wonder if the hand warmer wasn't giving off water vapor or something.

Hot water is a good solution. Fill a bladder for a pillow and one for your core in the bag. Extra fuel yes but if you are rested you can carry it.