Open it, shake it, and let your worries dissolve away as the heat builds up. With a 5-year lifespan, these hand-warmers heat up to 135°F (57°C) and are odorless, battery-free, and have a place in every backcountry skiers backpack. The air-activated formula fits well in most gloves and mittens, and provides several hours of artificial heat. Placing the hand warmer into an overmitt pouch on lightweight race-style gloves also yields good results. The Yaktrax Hand Warmers let you get away with more dexterous gloves. Each packet includes a pair of ambidextrous warmers.