Phase-change material

Phase-change material is a substance that can change from one form to another, like from a solid to a liquid or vice versa. For example, when you put a stick of butter in the fridge, it changes from a soft, liquid form to a hard, solid form. This is because the temperature changed and caused the butter to go through a phase-change. Phase-change materials work the same way, they just change form at temperatures that are much higher or lower.