Styrofoam trays are made from #6 Polystyrene, and they're used mainly because they're relatively cheap and lightweight. They're also very convenient, requiring no maintenance. However, Styrofoam is made from a nonrenewable resource, petroleum, and produces toxic chemicals during production. It is also nonbiodegradable and, for the most part, nonrecyclable. Disposal is limited to the landfill or incineration, which releases toxins and greenhouse gases into the atmosphere. There are concerns that toxins can leach from the trays when heated or exposed to hot food.
Plastic trays are sturdier and washable, which means after the initial purchase investment, a plastic tray could be reused thousands of times. However, with increasing water shortages and limited funds, schools often find it difficult to afford dishwashing machines, the extra water for cleaning the trays and the additional labor required from lunch staff to run the dishwashers, plus dishwasher maintenance and dish detergents. Dishwashers without dryers mean wasted time waiting for trays to air-dry, bringing down the efficiency of tightly timed lunch shifts. Dishwashers also introduce chemicals into waste water if non-eco-friendly detergents are used.
Both Styrofoam trays and plastic reusable trays have environmental trade-offs, so other key concerns would be the long-term goals of the school as well as its budget. If economic, facility or staffing considerations make reusable trays an unrealistic goal, there are also newer biodegradable tray options on the market, including plant fiber-based trays made from sugarcane, called bagasse, or wheatstraw. While these products are typically more expensive than Styrofoam at present, they may provide a compromise between disposable and reusable.