If you are short of time here is the description from Amazon for Heatmax HotHands:
Designed for skiers, hunters, fishermen, golfers, or anyone who works or plays in the cold for long hours, the Heatmax HotHands-2 Hand Warmers are air-activated and will provide up to 10 hours of soothing warmth inside gloves, pockets or wherever you feel a chill. All Heatmax warmers are made of natural materials, including iron powder, water, salt, activated charcoal, and wood fiber. When exposed to air, these materials react together to produce heat through an extremely fast oxidation (or rusting) process. Users should allow 10 to 20 minutes for the warmers to reach their optimal temperatures.