Is Styrofoam Microwave-Safe? Well, Sometimes…

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Last updated on March 12, 2023


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Not always. As with most things in life, there isn't just a simple yes or no answer. It depends. Sometimes yes, sometimes no. In certain situations, styrofoam can be harmful when microwaved, but how can you tell?

We are here to help you decipher what types of styrofoam can be microwaved, and when to transfer it to a different microwave-safe container instead. 

Let's take a look.

What is Styrofoam?

styrofoam circles

Let's start by understanding what exactly "Styrofoam" is.

Like many products that get generalized – such as "Kleenex" or "Band-aid" – the term "Styrofoam" actually comes from a brand: the Dow Chemical Company.

The original "Styrofoam" was a form of extruded polystyrene (XPS) – which is a type of plastic.

However, now the word "styrofoam" (without the capital letter) has been appropriated to mean any form of waterproof, light, and "puffy" plastic, including ones produced by a different process, such as expanded polystyrene (EPS).

What is "number 6 styrofoam"?

That's a bit of a trick question. All of what people call "styrofoam" is a form of polystyrene, which is plastic number 6 (in that little recycle symbol). So, in short, "number 6" styrofoam is all of it.

And, to be honest, plastic number 6 it isn't that good – not for the environment, and not for your health if you microwave it.

Despite the recycle symbol, you can't easily recycle it – at least not in the UK. Most local councils won't bother to recycle plastic number 6.

How to Tell if Styrofoam is Microwave-Safe


The best way to tell if a styrofoam container is microwave-safe is to look for the "microwave-safe" symbol. If it contains this symbol, then your styrofoam defies the odds, and you're free to nuke it.

There are various symbols to look out for. 

However, not all styrofoam products have this symbol. If your container doesn't have the symbol, or you're unsure if it does, then it's safer to first transfer your food to a ceramic or glass container or plate before microwaving. 

Which Styrofoam is Safe to Microwave?


The most common types of "styrofoam" are EPS and XPS. EPS is generally used for food take-out containers. And, unless it says otherwise, microwaving EPS is generally a bad idea.

Heating EPS releases styrene, which is a known carcinogen. It may then leech into your food. This is better avoided, if possible.

Is Genpak Styrofoam Microwave-Safe?

The brand Genpak has a number of containers that it sells as "microwave-safe," but this is not all of them. So don't assume so and transfer it to another container, unless you see a microwave-safe symbol.

What Happens if I Microwave Styrofoam that isn't Microwave-Safe?

You aren't going to die. However, polystyrene can leech out carcinogens, and it won't be good for you in the long run. If you microwave a styrofoam container that isn't labelled for that use...just don't do it again.

Can You Microwave Styrofoam Takeout Boxes?


Unless there's a clear symbol indicating that you can, that would be a risky endeavour. Take the extra time to transfer it to another container – and, ideally, not a plastic one.


As you can see, there are microwavable styrofoam containers, but they aren't the norm. So if it's an unmarked container, better be safe than sorry and transfer your food to something that is microwave-safe.

Obviously, microwaving styrofoam once isn't going to kill you... but it's best not to make a habit of it.

We hope this guide helped with all your styrofoam questions...feel free to reach out if you have anymore concerns. We are here to help.

Jane Sofia

About the author, Jane Sofia

Jane Sofia Struthers is a self-taught vegan chef who’s always terrorizing kitchens of one continent or another. When she’s not culturing her own soy milk yogurts in the oven, she’s either cooking plant-based goodies for her Couch-surfing hosts or on the lookout for more delectable, animal-free goodies.