from the initial nucleation site and eventually causing the entire contained liquid to solidify, thereby releasing the thermal energy of the crystal lattice. The use of the metal disc was invented in 1978.

The pad can be reused by placing it in boiling water for a few minutes, which redissolves the sodium acetate trihydrate in the contained water and reconstites a supersaturated solution. Once the pad has returned to room temperature it can be triggered again. Triggering the pad before it has reached room temperature results in the