These biodegradable and compostable souffle cups are made from NatureWorks polylactic acid (PLA), which is derived from corn grown in the USA. Our cups meet the most stringent scientific requirements for biodegradability and compostability, and are ASTM D6400-99 certified for "compostable plastics". Even though they are as light and strong as plastic, they fully biodegrade when composted. Store below 110F and away from heat, hot surfaces and direct sunlight.