So is it safe to use any metal at all in the microwave? Well, you might not have noticed, but there already is a bunch of metal in your microwave. The walls and circuitry are mostly metal, and the door has a mesh built in that lets visible light out, but reflects microwaves back in. This shielding is important. Not only are your leftovers mostly made of water, but so are you, and it’d be a drag to cook yourself before the meatloaf’s done. (Microwave burns are a real thing, but you have to turn to fiction if you want extreme microwave havoc: Infinite Jest tells of a grisly head-in-microwave suicide.) On a smaller scale, faulty shielding can lead to microwave bursts strong enough to fool radio telescope astronomers.


If you must put metal in your microwave—your house, your rules—the safest option is flat, non-crinkled aluminum foil. With few sharp corners, the electrons have a large area to vibrate over and not many places to get stuck. Sparking isn’t a problem, and the microwave reflections can shield food and keep it cool, like a blanket over a chicken bone you want to protect from burning. Limit yourself, though. The USDA suggests covering no more than one quarter of your food, keeping excess reflections at bay. Thin, flat foils are also part of “crisper” packaging like Hot Pocket sleeves and frozen pizza trays. These foils reflect microwaves, concentrating the energy nearby and cooking the crust a bit more than the rest. (It’s all relative, though. You’re never going to get a nice sear on a microwaved steak, crisper foil or not.)

Beyond that, be wary. Spoons are smoother than forks and should lead to less sparking, and a metal mixing bowl might likewise be cornerless enough, but when you’re explaining what happened to the insurance claims officer, don’t say you heard that justification here.