MINNEAPOLIS (WCCO) — Brandon from Shakopee wants to know: “What makes hand warmer packets so hot?” Good Question.
The outer wrapping of the warmers keep the packets from being exposed to air. Once the packaging is open, the covering of the packets are breathable and allow for the contents inside to be exposed to oxygen.
Inside the packets is iron powder, salt, charcoal, vermiculite and water.
When the packet is exposed to oxygen, it oxidizes the iron, creating rust and heat. The salt speeds up that reaction and the charcoal spreads the heat around. The vermiculite keeps the heat from escaping too quickly.
The polypropylene helps hold in the water, so the reactions can continue to take place.
After a few hours, all of the iron oxidizes and the heat disappears.