Can I microwave food in my plastic containers?

By Susan Brewer, Ph.D., University of Illinois,
Department of Food Science and Human Nutrition
 
Most plastics were not designed to be used in the microwave oven. Those that are microwave-safe will say so on the bottom. In general, do not heat or reheat foods on foam (take-home) containers or food trays (disposable plates, meat trays), in margarine or whipped topping tubs, or in plastic wrap (unless it comes with a frozen-reheatable meal which directs you to do so). Plastic trays that hold microwavable foods are designed to be used one time, then discarded. The primary problem with using plastic packaging in the microwave is that it doesn’t tolerate the heat. It will warp and in some instances allow chemicals used to manufacture the plastic to leach into the food.
 
Source(s):
Clemson Extension. HGIC 3586 “Microwave Food Safety”