Is Styrofoam Safe To Put In The Oven?

We all know about styrofoam, it will often be used as packaging for sensitive items in the post. It is also used for containers and cups.

It is very lightweight, and it is often used in restaurants, and it is often what makes up takeout boxes.

If you’ve been to a restaurant and decided to take your leftovers home, you are taking them home in a styrofoam box.

Can you reheat your food in these containers? Or, is that a bad move? 

You wonder if you can put your styrofoam container in the oven to heat up your food, or if you are better off just plating up before you reheat it. Well, don’t put styrofoam in the oven.

Styrofoam is made from expanded polystyrene, and it does not withstand heat well. It will start to soften at 212 °F, and it will melt at 464 °F. You can use styrofoam containers to preserve food in the fridge, but you can never reheat it or cook it in the oven. 

Today we will talk to you about styrofoam, what it is, how it reacts to heat and what the safe ways of using it are. 

What is styrofoam? 

Styrofoam is trademarked by ‘The Down Chemical Company’, which manufacture Styrofoam through the extrusion of polystyrene foam. In the USA, the word ‘styrofoam’ refers to a type of expanded polystyrene. 

Before we go any further, lets take a quick look at the differences between extruded polystyrene and expanded polystyrene. 

Extruded polystyrene is made through a manufacturing process that includes mixing it with other ingredients and then melting them together. 

Expanded polystyrene insulation, heat, or steam, is applied to molds filled with polystyrene beads. This causes them to expand and stick together. 

Polystyrene is a plastic material that is used in the creation of many products used daily, and it is derived from the monomer ‘styrene’. 

When it is turned into a foam-like material, polystyrene is most valued for its fantastic cushioning properties. This type of polystyrene is about 95% air, which makes it very buoyant. 

Taking a close look at a hunk of styrofoam you will see many white spheres. These are particles that have been expanded in order to form a particular object, cup, box or so on. 

These beads that you see in polystyrene are way smaller than the already expanded beads that you can see in a piece of styrofoam. If you have these beads at hand you could do a few experiments to get an idea of how styrofoam is actually made. 

If you were to put these beads into a kind of metallic mold that you can close tightly, filling it ⅓ of the way with them, then boil for a few minutes. When you remove the mold and let it cool you would see that the beads will have expanded quite a lot. 

Polystyrene beads also expand when microwaved with a small amount of water or steam. 

What is it used for? 

Styrofoam is used in many take out food containers, plates, and cups. This kind of packaging is every lightweight, and it is heavily convenient for cold food storage. 

It is the most common packaging for when you get your food picked up or delivered. 

How hot can styrofoam get? 

If you have held a styrofoam container in your hands and felt how lightweight it is, then you may be concerned about putting it somewhere hot.

It would feel as though the box would melt away into nothingness immediately. 

What is the melting point of styrofoam?

Since we know that styrofoam, is just polystyrene beads, we are looking at the melting temperature of these beads. And, the temperature at which these beads melt is 464 °F or 240 °C.

However, a styrofoam container will actually start to soften way before heat reaches this temperature. 212 °F is enough for a styrofoam container to start to soften. Remember this is the boiling temperature for water. 

Can you put styrofoam in the oven?

You cannot put styrofoam in the oven, as you can probably already imagine. There are two reasons for this. 

First of all, Styrofoam containers do not take this kind of heat all that well. Since they start to soften at 212 °F, they would not survive the reheating temperatures of an oven, which is generally around 320 °F to 350 °F.

If you were to attempt to reheat food in a styrofoam container at a temperature lower than 212 °F it would be pointless. It would also ruin the box and your food both.

Then, if you even could put styrofoam in the oven, you are never recommended to actually eat hot food for styrofoam containers anyway. 

Even though some restaurants put hot food in styrofoam containers, eating it like this won’t cause any irreversible damage. However, you should avoid doing this at home, and instead we recommend that you transfer your food into a suitable container instead. 

What would happen if you put styrofoam in the oven? 

Okay, so, let’s say that you have brought home some delicious leftovers from your meal at a restaurant. You decide you want to reheat it, and so you just pop the whole thing, still in the container, into the oven. What will happen? It will start to discompose. 

Leaving styrofoam in the oven at high heat will cause it to melt and turn into a soft and sticky mess. Would you like some food with your melted polystyrene? Some oils may come out of burned styrofoam as there is styrene in it too.

This is an organic compound and an oily liquid. For this to happen, your oven would need to be hot, very hot, to reach the melting point of polystyrene. 

What is safe to put in the oven? 

There are a few things that are safe for you to put in the oven, lets have a look at these, so that you know what things you can switch out for styrofoam. 

  • Metals. Cats iron and stainless steel are both safe options you can use for reheating food in the oven. 
  • Glass. You can get oven safe glass dishes and these are a great option. One of the things we love about these are that they can also be used to serve the food, so you cut down on how many things need to be washed after. You should not use pans or dishes that have any plastic or wood detailing on them though. 
  • Ceramics. You can also get ceramic dishes which can be put in the oven. Although, always be sure to heck the label in order to make sure that this particular dish is oven-safe. 

What happens if you were to accidentally burn styrofoam?

So, what if you were to accidentally burn styrofoam? Well, styrofoam releases dangerous chemicals when it burns. The gas and the chemicals that burned styrofoam releases are very toxic to the environment and to you as well in fact.

It can, in some cases, adversely affect your lungs. This is one common example of the effects of burning styrofoam. 

However, do not be scared if you have accidentally left a styrofoam container in the oven to heat a takeaway meal on one occasion. It happening once will not cause severe damage to your or to the environment. It’s when it is a more regular thing that it turns into a danger. 

What happens when you microwave your lunch in styrofoam? 

If you are hoping that the easy-peasy kitchen appliance will come and save the day. Don’t. Stop for your own sake. It is not often recommended that you put styrofoam anywhere near your microwave either. Don’t even consider it. 

You see, styrofoam containers, primarily made of polystyrene, will soften and release chemicals in a microwave oven just as they would in a standard oven.

Although, do note that microwave-safe styrofoam does exist, this type of styrofoam is made to withstand the microwaves in a microwave oven, and it is safe to eat food from too. So, check that this is what you have before you go chucking your food into the microwave oven. 

What is microwave-safe styrofoam? 

While traditional styrofoam containers are not safe for microwave usage, there are specific microwave-safe styrofoam containers that you can use, making things easier and safer too. 

These types of styrofoam containers are made with even safer materials that do not release chemicals when they are heated in the microwave. This being said, never assume that a container is or is not microwave safe.

What you should do is check to see a label on it that clearly states that your container, cup or whatever it is, is safe to be used in the microwave. 

If you cannot find the label, then to be on the safe side it is best to reheat your food in a different container that you know is microwave safe. It is much better to be safe than sorry in any situation. 

Microwave your food safely

If you are still undecided on whether or not you should put styrofoam inside your microwave it is best to do it in the absolute safest possible way you can. This means following some simple rules.

  1. Transfer your food from the styrofoam container and onto a plate, or into a container that you know if microwave safe, ceramics are a good choice. 
  2. Do not leave metal utensils in your food, this can cause sparks. 
  3. Spread the food out on the plate so that it heats evenly and reaches a definite safe internal temperature.
  4. Stir the food, or rotate the plate as you reheat a plate of very cold food in order to avoid any cold spots that may contain bacteria.

What can you use a styrofoam container for? 

Styrofoam containers are fantastic for storing your cold food in. You can always put your leftover in a styrofoam container and store it in the fridge. Styrofoam definitely deals better with cold than it does with heat. 

Styrofoam cups are also a fantastic container for cold drinks. You should avoid using these cups for hot drinks if you can. While they may insulate a bit and keep hot drinks hotter for longer, and they may also be comfortable for holding.

They are not recommended for use with any hot liquids, not only are they a bit squishy but if a drink is hot enough it might have a similar effect to a low powered oven. 

You should also avoid using styrofoam containers for any acidic foods. A hot dish with tomato sauce as an example should not be eaten from a styrofoam container. 

This also applies to drinks that are highly acidic too, such as strong citrus juices, or cocktails. These should instead be drunk from cups that are made from other, more resilient materials such as glass, which is an elegant and sustainable choice. 

We would also suggest avoiding the use of foam polystyrene cups for alcoholic beverages. We also avoid food and drink types that are traditionally eaten from or stored in bowls, plates and containers that are traditionally used for oily foods. 

Simply put, you can use a styrofoam container and cup for anything, as long as it is not acidic, oily, alcohol-based, or hot. And, after our overall summary, we can all agree, you should not put styrofoam in the oven, It will ruin your food.

Frequently Asked Questions

What Temperature is Safe for Styrofoam?

You should not put styrofoam containers in the oven as it is made from expanded polystyrene and will not withstand the heat. This material will start to soften at 212 degrees Fahrenheit and start to melt at 464 degrees Fahrenheit. You can go ahead and store food in styrofoam containers to preserve food in the fridge, you cannot reheat your food inside of this packaging.

Styrofoam has a maximum safe temperature of 175 degrees Fahrenheit, and it will start to warp at around 22 degrees Fahrenheit, which is boiling point. However, it does not have a fixed melting point. Sometimes, additional chemicals will be added to the material to ensure that it is safe for microwave use by allowing it to withstand higher temperatures.

So, if you are not going to be heating the styrofoam to higher than 175 degrees, then you shouldn’t face any problems. However, you likely are not going to be able to achieve this with a microwave.

Does Styrofoam Release Toxins When Heated?

Something that you might not have known is that styrofoam contains toxic substances, like Styrene and Benzene, which are suspected carcinogens and neurotoxins that are known to be hazardous to humans. Hot food and liquids will actually start to break down the styrofoam, which can cause some of the toxins to be absorbed into the bloodstream upon consuming these foods. 

Styrofoam food containers can seep styrene into warm foods, alcohol, oils, and acidic foods. This can cause contamination and pose a health risk to people. This is the reason why you should avoid drinking tea that contains lemon, which is acidic, out of styrofoam cups. You also shouldn’t consume alcoholic drinks or fruit juices out of styrofoam cups. Another thing to avoid is eating really oils foods out of styrofoam containers.

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Cassie brings decades of experience to the Kitchen Community. She is a noted chef and avid gardener. Her new book "Healthy Eating Through the Garden" will be released shortly. When not writing or speaking about food and gardens Cassie can be found puttering around farmer's markets and greenhouses looking for the next great idea.
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