Many pre-made microwavable products use metal to direct/control heating. The most well-known is probably "hot pockets", which use a metal-lined sleeve known as

Many pre-made microwavable products use metal to direct/control heating. The most well-known is probably "hot pockets", which use a metal-lined sleeve known as a "susceptor". https://en.wikipedia.org/wiki/Susceptor https://en.wikipedia.org/wiki/Susceptor