Microwave - Metal Cavity

All microwave cavities are made of metal. The interior is either stainless steel or painted steel with a special microwave paint coating. 

 

Convection models happen to be made of stainless steel for easier cleaning. Furthermore, the walls are not painted like typical microwaves are since they can heat up over 400 degrees Fahrenheit in convection cooking mode.  Metal is the only material that will contain microwaves so all microwave walls are metal. The mesh screen (called a choke) you see in the window is also metal to keep microwaves from passing through the glass or the plastic door.

 

All microwave cavities are "tuned" to a specific size and configuration, as are the metal racks that come in some models. Adding metal utensils into the cavity disturbs the planned pattern of the microwaves and can cause arcing from the metal object to the nearest grounded object which is usually a wall.