A susceptor for heating a food substance in a microwave oven is disclosed which has a thin film of metal deposited on a dimensionally stable dielectric substrate, such as paper. Substrate having a rough surface may be used. Preferably, the susceptor has a complex impedance measured prior to heating, at the frequency of the microwave oven, which has a real part between 30 and 2000 ohms per square. The preferred thickness of the thin metal film is related to the smoothness of the paper substrate. A substrate having a surface smoothness, expressed as an arithmetic average roughness, greater than 0.5 microns may be used with the present invention. The metal film is preferably aluminum having a thickness between 50 Angstroms and 600 Angstroms. The substrate may be coated with coatings such as clay. Clay coated paper substrates having a thin film of metal deposited thereon exhibit improved stability of performance characteristics during microwave heating.