Heat Factory’s pack of 40 pairs of adhesive Toe and Foot Warmers are designed for use on cold feet and when wearing shoes, boots and other air-restricting footwear. Heat Factory's Toe Warmers provide up to 6+ hours of reliable, even heat. The Toe Warmer features an adhesive backing that adheres to the outside of a sock underneath the toes. The design of the warmer is ultra-thin, to ensure comfort and an even form under the foot. The Heat Factory Toe 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. Proudly designed and hand-made in the USA, 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.