Polyester compositions are disclosed that include polyester polymers or copolymers having incorporated therein carbon-coated iron particles that improve the reheat properties of the compositions. Processes for making such compositions are also disclosed. The carbon-coated iron particles may be incorporated in the polyester by melt compounding, or may be added at any stage of the polymerization, such as during the melt-phase of the polymerization. A range of particle sizes may be used, as well as a range of particle size distributions. The polyester compositions are suitable for use in packaging made from processes in which a reheat step is desirable.