Thermic Heated Insoles.....I purchased some battery operated insoles for my Dad a few years ago and he likes them. I got a pair also, but have only used them a few times. It has to be really cold for me to need them. Each side has a long wire from the heel that comes out the top of your boot and plugs in to a 4 AA battery cartridge with a pocket clip. I keep the two cartridges in my pack and hook them on my boot tops and plug them in if needed. I believe they have three heat settings.