If the local food is wrapped in tin foil, it will reflect the microwave from a certain angle to prevent the food from overheating and burning. The barbecue device in the microwave oven uses the thermal infrared rays emitted by infrared heating tubes to heat food, but tin foil is a very bright metal, so it also has the function of reflecting light waves. Eventually, the heated object can't get energy, which leads to undercooking.