Ergodyne n ferno hand warming packs are self contained packs that provide heat anywhere to activate just open the pack and it will warm up once exposed to air the packs contain natural ingredients that heat up once exposed to oxygen the packs can be placed in an air tight bag to allow them to be reused the next day they will provide up to 8 hours of warmth great for placing in gloves pockets and inside winter clothing ideal for the following applications construction freightbaggage drilling mini