Metallic materials totally reflect microwaves

Microwaves may either be reflected, transmitted or absorbed by matter in their path. Metallic materials totally reflect microwaves. Most non metallic materials such as glass and plastics are partially transparent to microwaves. Material containing moisture, such as food and even people, absorbs microwave energy. If energy is absorbed at a rate greater than the rate at which the material looses energy (ie. rate of cooling), its temperature will increase.