There are herein described phase change materials containing sodium acetate trihydrate having improved homogeneity, a process for the preparation of said materials, and their utility in phase change systems. More particularly, the present invention relates to the use of phase change compositions comprising sodium acetate trihydrate, at least one alkali soluble polymer for inhibition of sodium acetate anhydrous crystal formation in sodium acetatetrihydrate containing phase change materials, and at least one sodium acetate trihydrate nucleation promoter, and, if a lower phase change temperature is required, at least one melting point depressing agent.