Microwaves are so efficient that they reduce our energy needs. They are designed to heat the food within the polystyrene container not to heat the actual container. If the food within the container gets too hot this will cause the container to soften which may present a safety hazard for handling. Microwaving polystyrene containers will not hurt anyone who uses them. If the container collapses, the food within the container may not taste very good. Best practices should be followed in order to microwave polystyrene properly.
Polystyrene doesn’t melt from the heat in the microwave. The microwave works by creating a rapid motion with molecules, like water. The collision between these rapidly moving molecules create frictional heat, first within the liquid water, which is then transferred to the entire food or beverage. Since polystyrene products are 90% air, polystyrene is actually transparent to microwaves.
Myths about Microwaving:
Fun Fact: Microwaving containers that are round or oval shape can help heat food evenly. With rectangular containers, the corners tend to receive more energy, which can cause the food the dry out or overcook.
Bloomfield, Louis A. How Things Work: The Physics of Everyday Life. New York: John Wiley & Sons, Inc., 1997.
Breder, Charles V., PhD. Common-Sense Approach to the Use and Reuse of Food-Contact Plastics to Heat & Reheat food in Microwave Ovens. Washington, DC: American Plastics Council. (www.plastics.org, 2002)
Meadows, Michelle. “Plastics and the Microwave.” FDA Consumer Magazine. Washington, DC: U.S. Food and Drug Administration, November-December 2002.