These are the clear vinyl pads, which start with a liquid inside. You find a little metal disc, which you squeeze. This sets off a chain reaction, the whole contents becoming crystalline and hot in a few seconds. Having warmed your hands you then have to boil the pad for 15 minutes to re-liquify the contents and start all over again. I can't find anything on Google or Ask about them - anybody know what is the liquid and how does it work?