A top choice of athletes, skiers, campers, hunters, anglers, spectators, construction workers, and more, the Yaktrax Foot Warmers provide a safe, long-lasting heat source so you can stay outside and enjoy the great outdoors longer Fits women's shoe size 9+ men's size 8+. Includes 2 warmers per pack. Provides up to 5 hours of safe, natural heat. Air-activated and odorless. Environmentally friendly. Contents: iron powder, water, salt, activated charcoal, and vermiculite. Average activated temperature: 105degF (40degC)