I have here a product called ‘HotHands’ (nothing to do with sex, so get your minds out of the gutter) that is primarily sold to hunters, football fans, etc. to keep hands, feet, and other body parts warm during cold weather. The product consists of a small sealed pouch containing, according to the label, Iron Powder, water, salt, activated carbon and vermiculite. The instructions are to shake the pouch to mix and activate the contents, which will then generate heat for up to 18 hours, minimum 104 degrees, maximum 154 degrees, average 130 degrees. They do work, although I can’t verify the actual temperature, as I’ve used them during our recent severe cold spell to protect some water pipes.

Can anyone tell me how/why this mixture produces heat? And why doesn’t it become ‘activated’ during ordinary shipping and handling?

In a nutshell, the Iron rusts really quickly and generates heat.

Thanks, Shiva - that’s perfect!

A teensy bit more ignorance eradicated, courtesy of Shiva!

You used them for water pipes? Neat idea, but kinda expensive, no? Why not just open the cabinet doors under the sink and run the water? Or aim the blowdryer in there? Or the outlet from the canister vacuum cleaner?

How cold was it, anyway?