Can You Microwave Styrofoam?

You may be wondering if you can safely microwave Styrofoam. The answer to this question is maybe. In reality, it’s a complicated issue. To understand whether or not you can safely microwave Styrofoam, we will need to go into the details of Styrofoam and understand what makes it a possible danger and how to protect yourself from this danger.

Defining Styrofoam

Before we being, it’d be helpful to get a precise definition of styrofoam. Styrofoam is technically a trademarked term, referring to a specific brand of a type of material called extruded polystyrene foam. While Styrofoam is officially created for use in insulation for buildings, colloquially the term is used to refer to any type of polystyrene foam or the white polystyrene foam used to hold food products and used as packaging material.


Polystyrene is the primary material used in the construction of styrofoam and it’s a hydrocarbon polymer, derived from a monomer called styrene. Polystyrene is heavily used in a number of different industrial applications because it is malleable and can be used to create many different forms of products. Examples include packaging peanuts, food containers, trays, disposable utensils, and bottles. Unfortunately, polystyrene is non-biodegradable and takes hundreds of years to degrade.

As mentioned, styrofoam, or polystyrene foam, is a type of soft plastic. There is no one substance called plastic, and some plastics can be safe to microwave while others are not. It’s unwise to microwave some types of plastic because the act of heating these plastics can release toxic chemicals that are used to help stabilize the plastic, which can then get into your food. Eating these foods can potentially harm your body over time.

The Hazards Of Endocrine Disruptors

Various chemical substances are added to batches of plastic in order to help stabilize the plastic or help it take on certain shapes. Two specific plasticizers are chemicals called bisphenol-A (BPA) and phthalates, which are used to make plastics clear and flexible respectively. Research into these chemicals has found that they might the endocrine disruptors, meaning that they are mistaken for certain human hormones by the body and as a consequence can disrupt your body’s hormonal balance, leading to various medical conditions.

Photo: Clker-Free-Vector-Images via pixabay, CC0

The endocrine system is made out of various glands that control hormonal balances, and these balances are necessary for things like proper tissue function, growth, proper metabolism, sexual function, mood regulation, and sleep. The endocrine system is made out of organs like the thyroid gland, the adrenal glands, the pancreas, and the genitals. The FDA’s website explains that endocrine system disruption can lead to various health problems, including developmental malformations (for those affected while still developing), problems reproducing (sterilization), increased risk for various cancers, and general disturbances of the nervous system and immune system.


Foods placed in a plastic container or wrapped in plastic wrap should not be microwaved because these substances can out-gas and leach into the food they contain. The migration of these substances is likely to be more severe when the food inside the container is fatty in nature like cheeses and meats. Because of the dangers, the FDA mandates that manufacturers of plastic containers test their containers to meet FDA specified product standards, ensuring the potential for plasticizer migration is kept at a minimum. These companies are required to provide the FDA with the test data before the containers can be released onto the market (if the product is intended to be microwave-safe).

How Do You Know If Styrofoam Can Be Used In The Microwave?

Various tests are run on the containers to ensure that they are safe to microwave food in during ordinary usage. Estimates are made regarding the average amount of time someone is likely to heat the container, how often the containers likely to be used, and how hot the food inside is likely to get. The maximum amount of plasticizers that are allowed to migrate is roughly 100 to 1000 times less per pound of body weight than the amount that has been demonstrated to harm lab animals. Only containers that meet these conditions can be marked “microwave safe”.

So if a container has passed FDA testing and is marked microwave-safe, you can be fairly confident it genuinely is safe to use in the microwave. Yet what about styrofoam? Can styrofoam be used in the microwave? While many people think styrofoam can’t be used in the microwave at all, styrofoam can actually be designed for use in the microwave. You simply need to check and make sure that any styrofoam container you are using the microwave is labeled safe for usage.

Photo: Clker-Free-Vector-Images via Pixabay, CC0

It’s important to note that the vast majority of styrofoam containers like coffee cups, styrofoam plates, and take-out containers are probably not microwave-safe. According to documents published by the National Institute of Standards and Technology, polystyrene begins to decompose at around 200°C, while pure styrene begins to decompose around 175°C. However, they begin to change states at lower temperatures, approximately around 100 degrees Celsius for polystyrene.

While the average cooking temperature of a microwave is unlikely to reach these temperatures, some substances contained within styrofoam may reach beyond these temperatures.  Water will need to be heated to around 100 degrees celsius to boil, meaning that at that temperature the styrene could degrade and mix with the water.


In addition, many styrofoam containers aren’t pure styrofoam, and it’s unclear how styrofoam containers created with other materials can affect the integrity of the styrofoam. For these reasons, if the container you are using is not explicitly marked microwave-safe, or if you are still worried about the possible harms of using styrofoam, it is recommended that you transfer your food to a glass, pyrex, or ceramic container to microwave it.

Comments (2)

  1. Following the logic presented in this article, pouring boiling water into a styrofoam cup would be hazardous. too. Yet, I don’t recall that ever being a concern.



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