Abstract: A composite material useful for controlled generation of heat by absorption of microwave energy is disclosed. The material comprises a dielectric substrate, e.g., polyethylene terephthalate film, coated with a mixture of an electrically conductive metal or metal alloy in flake form in a thermoplastic dielectric matrix, e.g., a polyester copolymer. In a preferred embodiment, the coating of flake/thermoplastic is applied so as to yield an isotropic coating with good heating performance reproducibility. The use of circular flakes with flat surfaces and smooth edges contributes substantially to good heating performance reproducibility.