I just moved to a cold climate and have to walk 3 miles each way to work. I have awful hand circulation and was worried that my commute would give me frostbite. These things are amazing! I stick them inside my pop top gloves and my hands stay toasty, no matter what the outside temperature. Tip: they release heat when they react with oxygen in the air; you can make them last longer (for me, 2-3 days) by storing them in a ziploc, if you're careful to push the air out. One note: they do get warm, so it's best to keep a thin layer between the hard warmer itself and your hand.