Can You Microwave Styrofoam? (Updated 2018)

There comes a time when we question whether or not it is safe to use a microwave to heat certain things.

Common knowledge says that materials such as metals (including aluminum foil) and most plastics are not meant to be microwaved and are potentially hazardous to one's food and ultimately one's health.

Can you microwave Styrofoam? In the case of plastics, it’s said that some types can be manufactured in a way that allows for usage in a microwave oven. Styrofoam is a type of plastic which is argued to be among those that are not normally microwave-safe, but that can be manufactured for microwave use as well.

Is it okay to microwave Styrofoam? We don't recommend it. In this guide, we will look at the dangers, possible effects and how they may outweigh the benefits of heating Styrofoam.

Types Of Styrofoam Containers

Styrofoam Containers
  • Coffee Cups - Often Styrofoam coffee cups are used to serve coffee and hot chocolate. They have also been used a cheap alternative to small bowls for serving soups, stews, and chili.
  • Styrofoam Plates - These are cheap alternatives great for parties since they are cheap and disposable, but are often used to reheat food on the following day or people who have simply arrive late to the event.
  • Cup Noodles - Why can’t you microwave cup noodles? Classic cup noodles typically have two sets of directions. One for simply adding boiling water, while the other may suggest filling with water from the tap and placing the entire thing in the microwave.
  • Take-out Containers - These are often used when ordering out or taking leftovers home from a big meal at a restaurant. Instead of removing the contents and reheating the leftovers on another dish, it’s much easier to toss the whole thing in the microwave for 5 minutes.

Is Styrofoam Toxic? The Chemicals In It

polystyrene symbol

What is Styrofoam made out of? One of the main chemical components of Styrofoam is Polystyrene which contains toxic molecules of styrene and benzene. They are chemicals that have shown potential carcinogenic and neurotoxic properties along with other detrimental side effects.

So the heated chemicals debate comes down to whether or not polystyrene is leeching chemicals into our food when heated by a microwave oven.

The National Institute of Standards and Technology (NIST) have published many reviews that indicate polystyrene started to show signs of decomposition around 200 degrees Celsius and showed small trace amounts of polystyrene being released.

Where it gets scary is around 224 degrees Celsius where polystyrene starts to break down. For pure Styrene, the temperature is about 175 degrees.

You don’t want to be cooking anything in Styrofoam at those temperatures! Cooking a pot roast in the microwave on Styrofoam is out of the question.

melted Styrofoam

Microwaving plastic at those temperatures will most definitely melt the plastic.

Does Styrofoam melt? Yes, it melts in acetone and when microwaved too long or with extremely hot food or substances. This is what happens if you microwave Styrofoam with Easter peeps:

Learn how to clean a microwave with lemon and water to help clean up various cooking disasters.

Let’s take a cup of water as an example. Water boils at 100 degrees Celcius (212°F) which is well below the point in which polystyrene has been recorded to release some of its self. But let’s say we’re getting some polystyrene into our cup of water because the cup has melted.

If the cup weighs 5 grams and you are ingesting 10% of that cup, you would be ingesting about 500mg of polystyrene. The EPA suggests that for styrene that would be about the upper limit of what’s considered safe in the short term.

As for Polystyrene facts, we were unable to find the data. But if the cup melted and you weren’t chewing on pieces of melted Styrofoam, there is a good chance that there is styrene somewhere in there on its own.

But these two chemicals are not the only ones to worry about. Depending on the manufacturer, they have added other chemicals to their Styrofoam in efforts to reduce costs or create a “better” product that may break down at lower temperatures.

Styrofoam Dangers & Side Effects

Is Styrofoam flammable? Pure Polystyrene is highly flammable, but depending on the application, chemical additives help it become more resistant to flame.

Unfortunately, Styrofoam containers are thin and not designed to be cooked with, therefore also poses a fire risk.

Some of the potential consequences that can result from ingesting the chemical components of heated polystyrene may include:

  • Eye and stomach irritation
  • Headaches
  • Fatigue
  • Hearing loss
  • Clinical depression
  • Dysfunction of the central nervous system

Does microwaving Styrofoam cause Cancer? You may have come across articles stating that Styrene, a chemical found in Polystyrene, has been linked with cancer. And to be clear, it has been listed as a possible carcinogen.

As the risks of microwaving Styrofoam are largely unproven at this point, it is hard to say whether or not microwaving typical Styrofoam releases enough of these chemicals to cause harm to human health.

Benefits Of Microwaving Styrofoam

In contrast, microwaving Styrofoam can also provide a few benefits.

  • Convenience
  • Cost-effectiveness
  • Disposability

Whether or not these benefits outweigh the risks is up to each individual.

How To Tell If Styrofoam Is Microwave Safe?

If your container doesn’t have a microwave safe symbol, we don’t recommend putting it in the microwave. Not even for 20 seconds!

Microwave Safe Symbol

The microwaveable symbol looks like a microwave with wavy lines. Because Styrofoam products are manufactured all over the world, the standard symbol can vary. However, you’ll want to look for something like the image above.

Can You Put Styrofoam In The Microwave Safely?

Since there is little data to suggest it’s completely safe to put Styrofoam in the microwave, we don't recommend heating it at all. There are many other options available, and your health should be more important than convenience.

Styrofoam substitutions to consider:

  • Glass or Pyrex plates and bowls
  • Ceramic plates
  • Skip the microwave and use a pot or pan for heating food or drinks

For the sake of your food and your health, be cautious about what you inside your microwave oven.

Microwaving plastic is not something we feel comfortable with so it would also apply to Styrofoam. To be on the safer side of things, when in doubt, don’t do it.


Did you enjoy this guide? Let us know in the comments below if you put Styrofoam in the microwave with your thoughts and any facts or safety concerns you have.

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Can You Microwave Styrofoam? (Updated 2018)
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