The present invention relates to a process for thermoforming a foamed polyester sheet of low crystallinity to produce a heat-resistant molded foam article (13). The process comprises the steps of heating a foamed polyester sheet (10) to a preforming temperature by contact with at least one heating plate and molding the heated foamed polyester sheet onto a non-heated mold (30). The present invention further relates to a process for manufacturing a package by thermoforming a foamed polyester sheet of low crystallinity to produce a heat-resistant molded foam container, loading a product (51) into said container and sealing or welding a film of thermoplastic material (61) onto said container to close it.The heat-resistant molded foam articles and the packages thus obtained are excellent in heat resistance and are not thermally distorted even when heated in a microwave or conventional oven. They are particularly useful for the packaging of food products for dual ovenable applications.