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How Hand Warmers are Made

What’s inside a hand-warmer? Wonder no more.
posted: 10/24/2011
Hand Warmers
by Kevin Luby

Admit it. You’ve used them. Don’t be ashamed. When the slopes turn into an icy hell, hand-warmers provide welcome relief. But they aren’t magic. A hand-warmer’s air-activated instaheat is more 10th-grade chemistry than high-tech trickery. In case you slept through class, here’s the fire behind Little Hotties Hand Warmers.

Iron Powder
Iron + oxygen + water = rust. The chemical reaction that turns iron into rust creates heat and is the secret behind hand-warmers.


When a hand-warmer is exposed to air, iron and oxygen ions combine, releasing energy. There is a tiny amount of water in the pouch that acts as the medium for the process to occur.


Salt, an electrolyte, improves the movement of electrons across water, speeding up the exchange between the iron and the oxygen. The result: instant warmth.

Activated Charcoal

Like a mini-barbeque, processed charcoal helps disperse the warmers’ heat, roasting your mitts.

A common fireproofer, vermiculite retains moisture and insulates, which is why your warmers are still cooking after five hours.

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