How Do Hand Warmers Work?

[Hollis987]

I refer to the type that look like large tea bags and contain hundreds of tiny beads. They start to warm up when the packet is opened and stay warm for at least 8 hours.

[janbee]

I suppose they work in a similar way to the heat pads one puts on sore old aching joints. They keep warm for a few hours.

[gingejbee]

There is a mixture of chemicals which, when exposed to air, start to react together producing heat (an exothermic reaction). The way the mixture is made (in bead form) means that the reaction is gradual - so heat is produced over a long period.