Fyi

[michika]

They seem to last about 8-10 hours, or at least this brand does. They don't get hot enough to be uncomfortable to the touch like say those therma bands do (for arthritis and back aches). I just stick them around the inside edges of the cooler/box and then keep them from touching the bags with newspaper.

I would show you a photo, but that whole damaged camera thing is a bit of a hang up. The ones I use however are called HotHands-2, and they come in a orange package. They are air activated. The ones for hands do not have a sticky strip, but the ones for boots do. I use the hands one and just tape on the edges, I try to make little tape stand-offs to ensure the air can circulate behind the pack.