Abstract: A foamed polyester resin article is made by a method which includes forming a molten resin mixture containing poly (ethylene terephthalate) having an intrinsic viscosity greater than 0.7 and a moisture content of not greater than 0.03%, a melt viscosity modifier which comprises a multi-stage emulsion graft copolymer of methyl methacrylate and a lower alkyl acrylate monomer, and a heat activatable decomposition-type foaming agent. The mixture is heated in the barrel of an extruder and extruded through the die of the extruder. The method can be used to produce extruded poly (ethylene terephthalate) sheet having a foamed structure suitable for subsequent thermoforming into packaging articles and food containers such as those used in dualovenable food trays used for reheating foods in microwave or conventional ovens. The articles produced by the method have a density which may be 35-40% less than that of similar articles made from conventional non-foamed poly (ethylene terephthalate).