Heat Factory 3/4 Length Ultra-Thin Foot Warmer - 5+ Hours Heat Each (24 Pair Warmers) 3/4-length foot warmer insoles designed to keep feet warm when skiing, hiking, and hanging out Heats up restricted air environment of shoe or boot for up to 6 hours Soft, lightweight pouches contain iron powder, charcoal, salt, water, and vermiculate Adhesive backing adheres to outside of sock underneath the foot; ultra-thin for comfort Not intended for use in open air; includes 24 pairs of foot warmer insoles