Susceptor

A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat (which in some cases is re-emitted as infrared thermal radiation).

This process raises the susceptor patch temperature to levels where it may then heat food by conduction or by infrared radiation.

For this reason, products meant to be browned via susceptor-generated thermal radiation carry instructions to microwave the food while still inside its packaging.

This is useful for crisping and browning foods, as well as concentrating heat on the oil in a microwave popcorn bag in order to melt it rapidly.

[1] A "crisping sleeve" is a device made of paperboard and affixed with a susceptor used both as a rigid container to support the food items within and to focus heat on the foodstuff.