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?
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.