Great to use with socks, footbeds, and in shoes and boots when hiking, walking, hunting, skiing and more, the Heat Factory Foot Warmers provide instant warmth to your feet in cold weather outdoor activities. The pack of 40 individually sealed Foot Warmers are designed to be placed in air-restricted areas like shoes, boots and slippers, socks and footbeds, for soothing heat to your feet. Each Foot Warmer provides 6+ hours of warmth. The Heat Factory Foot Warmer is a soft, lightweight pouch containing a biodegradable mixture of iron powder, charcoal, salt and vermiculite. When exposed to the air, an oxidation process takes place that generates heat. Heat Factory warmers are specially engineered to provide quality heat that is long-lasting, comfortable, and even. Heat Factory continually tests its products to ensure that you receive only the highest quality warmers that will consistently deliver warmth as advertised. Once activated, Heat Factory warmers can even be saved for later use (preferably within a week) if placed in an airtight container. Unopened, the Heat Factory warmer has a shelf life of three years or more. Heat Factory's air activated hand warmers, body warmers, toe warmers, and heated accessories have been providing warmth and pain relief to outdoor enthusiasts for the past 30 years.