The N-Ferno 6995 Insole Foot Warmers deliver up to 8 hours of warmth for the foot. They're flexible, moving with the foot to improve comfort. The thin and compact design prevents bulk and fits into any work boot or shoe, moving flexibly with the foot for all-day comfort. Full-coverage hot packs will provide heat for the entire foot. When done with the pad, simply toss and go. Each box includes 20 individually sealed pairs of warmers. HOW TO ACTIVATE These are air-activated heat packs, warming quickly when exposed to air. You can also shake the pack to speed up the warming process. Apply the feet warmers using the adhesive to the bottom of the feet. Then, slide feet into work boots or shoes for consistent warmth. Packs are not reusable and should be disposed of after each use (up to 8 hours). Adhesive foot warmers are ideal for those who work out in the elements such as those in construction, transportation, warehousing or delivery.