Abstract: Making foamed bodies by introducing a biodegradable polymer mixture into a mould (10) in which it is heated to form a foam and to fill the mould. The mould is defined between two opposed parts (12, 14) that mate together, and each mould part is of electrically conducting material, and the moulding surfaces are coated with an electrically insulating material (16). Radio-frequency signals are applied (25) between the mould parts (12, 14) so that the polymer mixture is heated by dielectric heating, so a foam tray is formed in less than 15 s. This provides a more rapid cycle time than using heated moulds. The radio frequency signals may be 27.12 MHz, or 40.68 MHz. The polymer may be starch-based.