microwave oven crisping grid
 

I don't understand how a microwave oven heats food. I don't understand microwaves. Is there a simple explanation how that sheet with gray lines in a grid makes pastry crispy when heated in a microwave oven?

Thanks,
Sixto
95 S420
87 300SDL

Short radio wavesx in the 2500 Mhz range heat the water in food. The gray stuff causes reflections. Too much metal in the cooking chamber causes high SWR in the transmitter and can lead to failure.

Small metal foil on plates and cups cause arching.