Things Should NOT Go into Microwaves

2. Aluminum Foil

Microwaves cannot pass through metal and are likely to cause sparks when reacting to it. Sparks do not damage microwaves if caught immediately, but prolonged appearance would. However, small amounts of aluminum foil can go into the oven to prevent over-cooking if followed the rule of thumbs, according to the USDA (Department of Agriculture):

• Cover the no more than 1/4 of the food with aluminum foil. Completely cover the food would damage microwaves. Neither would the food be heated.
• Use smooth foil. Wrinkled ones can cause sparks.
• Remove the foil immediately if sparks appear.