PSalt hydrates consist of inorganic salts and water. Their melt point temperatures range between 15°C and 80°C. The advantages of salt hydrates are low material costs, high latent heat storage capacity, precise melting point, high thermal conductivity and inflammability. The disadvantages:
Poor nucleating properties make them vulnerable to supercooling, the phenomenon in which a substance cools below its freezing point without solidifying. That can be beneficial in some applications, but for most uses nucleating agents must be added to address this problem.
The volume change in the solid/liquid phase change of a salt hydrate is up to 10%. Special packaging must be used to accommodate the changing volume.
Some salt hydrates fail to completely recrystallize following each cycle. Eventually, they lose all latent heat capacity.
Some salt hydrates are toxic and many are corrosive to metals, presenting safety and disposal issues.