Polystyrene is a lightweight transparent plastic derived from petroleum by-products and natural gas. It is widely used in the packaging industry, but most polystyrene is used to make durable goods such as television cabinets, appliances, and furniture. Polystyrene also has excellent insulating properties. As packaging, polystyrene is used both in foam and solid forms. Solid polystyrene is used in yogurt, sour cream, and cottage cheese containers, cutlery, clear clamshells used at salad bars, and video and audio cassette containers. As foam, polystyrene is used in cups, bowls, plates, trays, clamshell containers, meat trays, egg cartons, and packaging for electronics and other delicate items. Polystyrene foam is manufactured by processing solid polystyrene resin pellets with a gaseous expansion agent. In the past, about 30% of polystyrene foam products were made with chlorofluorocarbons (CFCs), which were identified as contributors to the deterioration of the ozone layer in the Earth's upper atmosphere...