meaning that a large amount of heat energy can be absorbed while the matter remains isothermic. Ice, for example, requires 333.55 J/g to melt, but water will rise one degree further with the addition of just 4.18 J/g. Water/ice is therefore a very effective phase change material and has been used to store winter cold to cool buildings in summer since at least the time of the Achaemenid Empire.

By melting and solidifying at the phase-change temperature