Abstract: A heat treating system comprises a hot-wall microwave applicator cavity having a gas-diffusing structure on one surface, a microwave power supply, a transmission line between the applicator and power supply, and a granular heat transfer medium partially filling the cavity. The medium may be a single material or a blend of several materials, preferably having equivalent aerodynamic densities. The related method includes the steps of: placing a material to be heated into a microwave cavity having a gas diffusing structure on one surface; partially filling the cavity with a quantity of granular heat transfer medium sufficient to cover the material to be treated and the gas diffusing structure; flowing gas through the diffusing structure at a rate sufficient to fluidize the granular medium; and, introducing microwave energy into the cavity to raise the material and granular medium to a selected temperature for a selected time.