Ergodyne - EGO16997 N-Ferno 6997 Adhesive Body Warmers adhere directly to clothing for up to 12 hours of warmth where you need it most. With an adhesive back, these air-activated heat pads can easily and securely be applied to base layers or the interior of jackets, gloves, hand-warmer muffs and more. To activate, simply open the individually wrapped pack. The all-natural ingredients will begin to heat up as soon as they are exposed to oxygen - no batteries required. You can also shake the pack to speed up the warming process. Warming packs help to regulate core body temperatures for safety in cold conditions. Warming packs should never be applied directly to the skin. These adhesive body warmers are not reusable and should be disposed of once warming effectiveness has worn off.