Yaktrax Foot Warmers are a safe, easy, and all-natural solution to dealing with cold feet. Once opened and exposed to oxygen, these disposable but environmentally-friendly warmers begin working in just minutes. Slide them inside your boots to create a warming barrier for your feet that lasts up to 5 hours. Yaktrax Warmers are the ideal choice for outdoorsman, winter athletes, spectators, and anyone who works or plays outdoors.