Heating up styrofoam: What you need to know

For all-out convenience in the kitchen, it doesn’t get much better than your microwave. The microwave’s ability to heat food or soften butter in seconds rather than minutes made it an instant hit when they became commonplace in American households in the mid-1970s.

But not every type of food container is meant for the microwave. Metal-based materials can’t be used in microwaves because the waves can’t penetrate through metal. With aluminum foil or tins, the microwave rays have nowhere to go, so the metal heats up really quickly and might eventually catch fire. With few exceptions, most glass and ceramic products are microwave safe, but they may not be practical for transporting or storing foods. So that leaves styrofoam. But can you microwave styrofoam cups or even heat styrofoam at all?

Read this before you put your styrofoam bowls, cups, or plates in the microwave.

What is styrofoam?

Trademarked by The Dow Chemical Company, the term ‘styrofoam’ actually refers to a type of polystyrene foam commonly used in the building industry. Over the years, the term has often been misused when referring to an expanded polystyrene foam that’s injected into molds to make disposable plates, cups, and take-out containers. 

Polystyrene containers are cheap to manufacture and are excellent at keeping foods and beverages warm, making them a popular choice in the food industry. But over the past several years, there has been a growing backlash against single-use polystyrene containers due to environmental and potential health concerns.

It can actually take about 50 years for a styrofoam coffee cup to decompose, and sadly, styrofoam and other plastics make up about 30% of all landfill volume in the United States. 

From a health perspective, styrofoam-based products contain a compound called styrene, which has been linked to cancers in animal and human studies. There is an increased risk of styrene leaking into foods when containers are microwaved.

Man looking into microwave ovenCan you safely microwave or heat styrofoam cups or other food containers?

Food-use styrofoam containers, made from expanded polystyrene, are not oven safe. These styrofoam containers will begin to soften at 212°F and actually melt at 464°. They are, however, safe to use for storing food in the refrigerator but never to cook or reheat in the oven. 

The Food and Drug Administration (FDA) does regulate plastic and polystyrene containers, cups, and plates and tests their safety and use in microwave ovens. Those deemed suitable receive a microwave-safe label indicating they have been tested for safety in the microwave. Look for the microwave-safe labeling on any styrofoam or polystyrene containers before putting them into the microwave.

“The FDA long ago recognized the potential for small amounts of plasticizers to migrate into food. So it closely regulates plastic containers and materials that come into contact with food. The FDA requires manufacturers to test these containers using tests that meet FDA standards and specifications. It then reviews test data before approving a container for microwave use.”

Harvard Medical School

A few more things regarding microwave reheating:

  • If you can’t verify that your styrofoam container is microwave safe, transfer the food to a glass or ceramic container labeled microwave safe.
  • If you want to cover foods while reheating in the microwave, use wax paper, parchment, or even paper towels. Don’t allow plastic wrap to contact food while microwaving, as it may melt during the heating process.
  • Those plastic tubs that hold yogurt, cream cheese, mayonnaise, and other foods may be tempting to use as extra food storage in the fridge, but they are not microwave safe.
  • Any plastic containers that are cracked, scratched, or microwaved many times can begin to leach out harmful plastic into your food. 

If you are unsure of your food containers’ microwave safety, don’t use them. By being diligent and reading labels, you’ll be able to enjoy the convenience of microwave heating while still keeping you and your family safe.

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