Can You Microwave Styrofoam?

Q. I have heard that you shouldn’t put styrofoam in the microwave. Is it true? If so why not, what happens? Can you microwave styrofoam? How about the styrofoam container with your leftovers from dinner last night, or the styrofoam cup your take out hot chocolate is in – can you reheat that in the microwave safely?

Can you microwave styrofoam?

Can you microwave styrofoam?

A. What most people know as Styrofoam, is actually the trade name of a polystyrene foam product used for housing insulation. Polystyrene is a petroleum-based plastic made from the styrene monomer and a lightweight material composed of about 95 percent air, with very good insulating properties. It’s used in all types of products from containers and  cups that keep your food and beverages hot or cold to packaging material that keep your computers safe during shipping.

Heating styrofoam in the microwave can cause it to lose it’s shape, or appear to melt. Polystyrene doesn’t melt from the heat in the microwave though, it would melt from the heat of it’s contents warming up. Styrofoam is a type of plastic, and toxic chemicals may leach out of these products into the food that they contain especially when exposed to heat. These chemicals threaten human health and reproductive systems and the effects of long term exposure are not fully known.

While you can put styrofoam containers in the microwave, the heat of it’s contents could melt the container and destroy your meal. Polystyrene (and most high molecular weight polymers) are in no way soluble in water, and even if 50 per cent of your cup were to melt, you will not be absorbing any appreciable amount through the water in your cup.

So what to do? Put simply, there are two basic types of Styrofoam, one is microwave safe and the other is not. If your container is marked as “microwave safe” go for it, and if not, move your food or drink to a glass, ceramic or otherwise microwave safe container.

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8 Responses to “Can You Microwave Styrofoam?”

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  1. Cheryl Van Epps says:

    Please check your usage of it’s, the conjunction of “it is” or “it has”. When you use “its” as a possessive, as in your sentence: “Heating styrofoam in the microwave can cause it to lose it’s shape, or appear to melt.” The word “its” does not require the apostrophe and should read “its shape”.

    Also, fatty and oily foods are commonly microwave re-heated in styrofoam containers. The heated oils can act as hydrophobic organic solvents causing focal melting of the styrofoam and leaching the monomeric styrene from the polystyrene.

    Note from an online physics forum: “microwaves heating oil: while a much poorer microwave absorber than water, oils still do absorb microwave energy and heat, especially if the quantity of oil is large – say 4 ounces or more. Also, oils have a specific heat capacity of about 0.5, which is half that of water (1.0) and that means that for a given amount of microwave energy absorbed oil will heat twice as much as water. But be extraordinarily careful heating oil inside a microwave oven because oils can easily reach temperatures of over 400 F! This can cause serious burns. So, it is best not to heat them inside a microwave oven.”


    No wonder my sausage and other fatty meats “explode” in the microwave!

  2. Scott Smith says:

    Cheryl, please check your use of “conjunction”. A conjunction is a word used to link two or more things. And, or, but are conjunctions.
    Compound words where an apostrophe takes the place of one or more letters are called contractions.

  3. Katie says:

    Can you microwave the styrofoam cups they have in the hospital?

  4. BigBillBMA says:

    If you are seriously correcting someone’s grammar and or punctuation on a post about microwaving food you are dull and boring get a life I am leaving all punctuation out of this just to piss you off

  5. nicole says:

    I wouldn’t microwave hospital styrofoam because, hospitals are in business because of sick people. I don’t imagine that they are concerned with providing patients with “microwave safe” styrofoam.

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