A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat (which is sometimes designed to be re-emitted as infrared thermal radiation). This energy is typically radiofrequency or microwave radiation used in industrial heating processes, and also occasionally in microwave cooking. The name is derived from susceptance, an electrical property of materials that measures their tendency to convert electromagnetic energy to heat.

In microwave cooking, susceptors are built into paper packaging of certain foods, where they absorb microwaves which penetrate the packaging. This process raises the susceptor patch temperature to levels where it may then heat food by conduction or by infrared radiation.

Susceptors are usually made of metallised film, ceramics or metals (such as aluminium flakes).

The susceptor (which may be located on examination from its gray or blue-gray color, which is different from paper) is the reason why products meant to be browned via susceptor-generated thermal radiation carry instructions to microwave the food while still inside its packaging.