You crack a metal disc in them to start the reaction and the whole thing turns solid. You normally need to boil them in water to reset them back to liquid for reuse.Interesting!
How do they work - some kind of reversible chemical reaction?
Interesting. May look tomorrow. Heard about cyclists using them in their shoes. How do you do this? (Serious question)
Interesting. May look tomorrow. Heard about cyclists using them in their shoes. How do you do this? (Serious question)