By Joe Jackson, Outside

Hand warmers—those small, usually disposable packets that provide on-demand heat—come in five main varieties, including some that run on charcoal and lighter fuel. The three most commons types you’ll see on the slopes are either air-activated, use a supersaturated solution, or are battery-powered.

All three can last anywhere from one to 10 hours. That’s a pretty broad range, and we wanted to find out which of these five popular hand warmers was the warmest and most useful for playing in the mountains.

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