The UnderWarmer is a Unisex, heated, bodywarmer undershirt designed to keep you warm all day. Integrated into the shirt are 8 large air-activate heat packs that stay hot for over 12 hours. Simply remove the shirt from its package and air activates the heat packs within minutes. Nothing you need to do but put it on. Worn as a base or second layer, it is perfect for outdoor cold activities such as hunting, fishing, camping, hiking, tailgating/football games, soccer moms, snowmobiling and countless other applications.