Metals including stainless steel and aluminum foil
Anything made of or containing steel, iron, copper or other hard metals should never go in your microwave. Metal surfaces reflect microwaves, which increases the heat inside the appliance and could lead to a fire. If you’re storing leftovers in a metal container, remove the food and place it in a microwave-safe container instead.
When it comes to aluminum foil, things can get tricky. Technically foil can be microwaved, but its surface needs to stay as flat as possible. Wrinkles or crumpled foil can cause “arcing”—that is, it can cause electric sparks to shoot across the surface of the foil, potentially damaging your microwave or causing a fire. In addition, food wrapped in aluminum foil may not cook or reheat properly in the microwave—the foil will reflect the radio waves instead. Each microwave is different, learn more about how a microwave works or consult your owner’s manual to determine if aluminum foil is safe. And when in doubt, avoid placing any kind of metal in your microwave.