How to Reheat Styrofoam
- 1). Check your container to be sure that it is Styrofoam. Plastics classified as polystyrene or Styrofoam are marked with a number 6 or the letters "PS." Styrofoam products tend to be white in color and rigid.
- 2). Inspect the container for a microwave-safe label. The package may contain the words "microwave safe" or display a symbol that looks like a microwave. Also check your Styrofoam to ensure that it is not cracked or broken, which can render the container unusable.
- 3). Heat your food in the Styrofoam if your Styrofoam container is marked as safe for microwave use. To avoid overheating the plastic, keep an eye on the food and heat for the least amount of time until the desired temperature is reached. If the container starts to deform, remove it from the microwave.
Source...