A hand warmer works based on a chemical reaction or physical principles that generate heat. There are different types of hand warmers, and their mechanisms vary depending on the type. Below are the three most common types of hand warmers and how they work:
Air-activated hand warmers
This is the most common type of disposable hand warmer. They contain a mixture of substances like iron powder, salt, charcoal, vermiculite (a mineral), and water. These substances are packed in a small pouch made of air-permeable material, usually non-woven fabric.
How it works
Once you take the pouch out of the packaging, the mixture comes into contact with oxygen from the air.
The iron in the mixture begins to rust (oxidation process) when it comes into contact with oxygen.
This oxidation process generates heat.
Vermiculite helps retain the heat and distribute it evenly, while salt speeds up the reaction.
These hand warmers can release heat for 1 to 10 hours, depending on the specific composition.
These hand warmers are simple to use and only need to be taken out of the packaging.
Disadvantages
They are single-use and cannot be reused.
Crystal-activated hand warmers (reusable)
These reusable hand warmers contain a solution of sodium acetate (a type of salt) and water in a plastic pouch. There is often a small metal disk inside the solution.
How it works
When you snap the metal disk, it triggers a chain reaction that causes the liquid solution to crystallize into a solid.
This crystallization process generates heat.
The hand warmer stays warm as long as the crystallization continues, usually around 30 minutes to a few hours, depending on the size.
To reuse the hand warmer, you need to boil the pouch in hot water to return the crystals to liquid form.
