hoes does a prince lionheart (on the -go) bottlewarmer works at a click of a button??

Question

its a baby bottle warmer in which you activate the bag by boiling, but after a feel hours or weeks later when the bag is even at room temp.when you need instant heat just click this little metal button inside and the clear gel or water inside starts turning like snow, but it's hot instanly like magic?
please explain

Answer 1

It sounds like they contain a material where you can induce rapid crystallization (which releases heat). I am assuming the bottle warmer is re-useable each time it is boiled to turn the solid material back to the liquid state.