Phase Change Material (PCM) is a substance with a high heat of fusion which, by melting and solidifying at certain temperatures is capable of storing and releasing large amounts of energy. PCM’s either absorb or release heat when the material changes from solid to liquid and vice versa. PCM’s are classified as latent heat storage (LHS) units. When a PCM is cold, it releases a large amount of energy at a relatively constant temperature. Conversely, when energy is applied, it absorbs a large amount of heat from the environment. Think of the PCM as a jelly bean – hard outer shell with a soft inside. The soft inside, absorbs and releases heat as conditions change, for temperature control.