Can You Put Styrofoam in the Microwave?

Styrofoam container in microwave

The professionals at Mr. Appliance® are sometimes asked, "Is it safe to put Styrofoam in the microwave?" And the safest answer is no. While some types of foam are labeled as microwave-safe, we don’t recommend using foam vessels for reheating food in a microwave oven.

Below is a more scientific exploration of the topic.

What Is Styrofoam?

Styrofoam is a registered trademark of Dow Chemical, but the term has become synonymous with all types of plastic foam material. The polystyrene foam used in takeout containers, packing peanuts, and other items is a petroleum-based material that is made from styrene and benzene. It’s popular because it’s lightweight, insulating, affordable, and long-lasting. However, applying too much heat to it can be problematic.

Is It “Bad” to Put Styrofoam in the Microwave?

Some types of foam are worse than others, so it’s not always that bad to put Styrofoam in the microwave, but you must be cautious. Start by knowing the differences between the two distinct types of foam containers on the market.

Traditional Styrofoam

It is not safe to microwave this most-common type of Styrofoam. During normal use, the material remains stable. But at high temperatures, it begins to melt or break down. Even if there’s no visible damage on the foam, a microwave oven may cause the toxic chemical styrene (among other chemicals) to leach into your food. Styrene is a possible carcinogen, posing a threat to your health and reproductive system.

Microwave-safe Styrofoam

A less common type of Styrofoam passes FDA requirements to be microwave-safe. This alternative material is constructed with safer materials and lower levels of hazardous chemical compounds, and it has greater stability when heated.

How do you tell if the Styrofoam is microwave-safe? Check the packaging for a clear label. Ultimately, it’s up to you whether you want to microwave this special type of Styrofoam or play it 100% safe. However, if you see any visible signs of damage to the Styrofoam after removing it from the microwave, discard both the food and the container. Additionally, avoid microwaving it if there are cracks in the foam or it’s been microwaved once already.

How to Reheat Food Safely

To fully eliminate the risk of polystyrene chemical exposure, use these methods of reheating food:

  • Microwave the food on a microwave-safe (non-Styrofoam) plate or in a bowl before reheating, covered with a damp paper towel to prevent splattering.
  • Reheat the food in your conventional oven using an oven-safe container covered with foil.
  • Reheat the food in a skillet on the stove, sprinkling a little water on top before putting the lid on. This works great for pizza!
  • Reheat soups and stews in a saucepan on the stove.

Don’t forget to follow general food safety guidelines, such as heating to an internal temperature of at least 165°F and never reheating food more than once. 

Finally, don’t use your microwave, oven, or stove if it shows signs of failure. Reach out to the speedy appliance repair experts at Mr. Appliance by calling your local team or scheduling service online.