The chemistry inside every hand warmer (since 1923)

Air-activated hand warmers use a simple exothermic oxidation reaction. When the pouch is opened, oxygen reaches the iron inside and the reaction releases heat.

What is inside

PREF*RE pouches use iron powder, salt, water, activated charcoal, and vermiculite.

Iron powder is the material that oxidizes. Salt and water help the reaction proceed. Activated charcoal helps distribute heat, and vermiculite helps hold the mixture in place.

Why the wrapper matters

The sealed outer wrapper limits oxygen. Once opened, air reaches the pouch and the warming reaction begins.

The ingredients inside can return to earth after use. The outer spun-lace pouch is not compostable.