The heat is created by chemicals, which activate when the packet is exposed to air. Some packets also must be shaken vigorously to get them going. The heat produced ranges from about 105 degrees to around 165 degrees, depending on the product. They are often effective from six to eight hours or more. Manufacturers recommend that the warmers not be placed directly against the skin.
Outdoor people find plenty of uses for the pads.
Herndon said that when he's backpacking, he likes to put them in his boots at night. Paul Soto puts a heating packet in the foot of his sleeping bag. Worn around the wrists, the bands hold hot pads. But don't forget your gloves. 2001 AzStarNet , Arizona Daily Star and its wire services and suppliers and may not be republished without permission.