Heating pads of this type from Rothco are no less than ingenious! When the cold bites too hard just get this little bag out of your pocket and break the little "coin" in the bag. This starts a chemical process that means that the bag slowly begins to exude a lovely comfortable heat that brings the feeling back into your fingers - or wherever you want it :-) {br] When you get back home, all you need to do is to boil the handwarmer and it will be ready for a cold outdoor trip again!