Phase-change material
![A sodium acetate heating pad. When the sodium acetate solution crystallises, it becomes warm.](/Images/godic/202502/02/Handwaermer123225.jpg")
![Phase-change material being employed in the treatment of neonates with birth asphyxia[81][82]](/Images/godic/202502/02/Miracradle3225.jpg")
A phase-change material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.