Some materials, such as styrofoam, are not microwave-safe and should never be microwaved.
Be sure to check your food packaging for microwaving instructions before popping that container of leftovers into the oven. Microwaves heat up food from the inside out, cooking it from the core through its surface.
What is styrofoam?
Styrofoam is a trademarked name brand of closed-cell extruded polystyrene foam. Styrofoam is а type of plastic and is manufactured primarily for thermal insulation purposes (walls, floors, and roofs) in the building sector and construction industry.
It’s made from polystyrene foam or plastic foam. Styrofoam has been also used extensively to package perishables and other products requiring a high degree of insulation. In fact, about 40% of the Styrofoam used in the United States is used for food packaging. 
Is it safe to reheat food in Styrofoam?
The answer is no. Styrofoam is not food safe, and reheating food in styrofoam may even lead to health problems. But what health risks are associated with reheating food in styrofoam?
Health risks associated with styrofoam exposure or intake are :
- Irritation of eyes and nose
- Hearing loss
- Nervous system dysfunction
Additionally, styrofoam tends to break down over time, which means pieces of styrofoam could end up in your reheated food.
Can styrofoam catch on fire in the microwave?
According to styrofoam.com, styrofoam cups can catch on fire in the microwave when in use for long periods of time with little water in it. For that reason, some styrofoam packages have a warning label that states “Caution: Do not heat this product…”
If styrofoam starts burning, it will start to release smoke and will shrink.
Can you microwave styrofoam?
Styrofoam is made of a substance called Expanded PolyStyrene Foam (EPS). It’s not safe to microwave any type of EPS, styrofoam or no styrofoam.
Styrofoam contains styrene, a chemical which can leach into food during microwaving at high heat. By eating the food, styrene particles may enter your body and cause various health risks. In fact, there have been reports (with limited evidence) of styrene being linked to cancer development.  .
How to Reheat Food Safely
There are many different options depending on how quickly you need to reheat food and what type of food you want reheated. Here is a list of quick reheating methods to choose from: microwave, oven and stovetop.
Microwaving styrofoam is not recommended because it may release toxic gases and start to melt (unless labeled “microwavable” and heated up to 212 degrees Fahrenheit). Styrofoam containers are made of polystyrene which decomposes, no matter how clean the container is when heated up.
Quick and safe ways to reheat your food are using oven, microwave or stovetop methods instead.