I bought a box of 40. I tried one to see how well it works. It claims average temperature of 126 to 144 deg. F. I folded one of the activated product around an electronic cooking thermometer; it built up to a max. of 100 deg. F. while surrounding the thermometer. It's not warm enough to do much good. I live at an altitude of 6400 ft. The air may be too thin at this altitude to heat correctly. I'm not satisfied at all.