Each warmer lasts up to 12 hours and provides fast heat that doesn't need to be recharged or reheated. Enjoy the ultra-thin and comfortable adhesive warmer by layer it between layers of clothes, not directly on the skin. They're safe to use, convenient to pack in a backpack or toolbox, and can be disposed of with regular trash. Grabber Warmers are made with natural ingredients that don't harm the environment and have a four year shelf life if stored in a cool, dry place.