Abstract: Compositions made up of one or more molecular alloys which are suitable for storing or restoring thermal energy at a temperature level T and over a time interval .delta. matching those required for a particular application as a phase-change material, said alloys belonging to a phase diagram having a transition region within a temperature range which includes the required temperature and has a near-horizontal geometric locus (EGC). Said compositions are useful as a phase-change materials, particularly in the agrifoodstuffs and paramedical industries.