The United States Department of Agriculture (USDA) lists containers considered safe to use in microwave ovens. They include any that are labeled for microwave use, heatproof glass like Pyrex or Anchor Hocking, glass-ceramic containers such as Corning Ware, and most plain white paper plates.
The USDA warns against using certain containers in a microwave oven. That list includes commercial storage containers such as margarine, cottage cheese and yogurt tubs, brown paper bags, foam, china with metallic ornamentation, or any container made from metal or that contains metal parts.
According to the American Frozen Food Institute, microwave ovens convert electricity into short waves. These waves penetrate the foods, and the friction caused by the rapidly moving food molecules generates heat. When cooking foods with a high fat content, the fat can get so hot that it can cause an unsuitable container, such as some plastics, to melt.
The Environmental Health Institute of Nova Scotia reports that a chemical called Bisphenol A, or BPA, is present in some plastics considered safe to use in microwave ovens. The study points to research done in 2006 by Frederick vom Saal, who theorized that microwaving food in plastic containers may increase the transference of BPA into food.