 Susceptors are usually made of metallised film, ceramics or metals (such as aluminium flakes).The susceptor (which may be located on examination by its gray or blue-gray color, which is different from paper) is the reason products meant to be browned via susceptor-generated thermal radiation carry instructions to microwave the food while still inside its packaging.Susceptors meant to heat foods by direct conduction in places where less browning will occur may be seen in the gray lining of packaging directly holding the food, and in good contact with it.