These clear biodegradable soufflé cup lids (only for foods below 110F) are made from NatureWorks polylactic acid (PLA), which is derived from corn grown in the USA. These compostable PLA soufflé cups are fully biodegradable and compostable and meet the most stringent scientific requirements for biodegradability and compostability, and are ASTM D6400-99 certified for "compostable plastics". Though, they are indistinguishable from normal plastic and as light and strong, they fully degrade into water, carbon dioxide and organic material when composted. There is no reason not to use these compostable cups made from readily renewable resources as compared to the petroleum based plastic cups, which create toxicity and environmental pollution. Please note that composting is required for biodegradation. These compostable souffle cups will biodegrade within 180 days in a commercial composting facility, but can take up to a year or more to biodegrade in a home composting system.