From a human and environmental health perspective, we believe that silicone is currently the best material available for snap-on, leak-proof food container lids because it's long-lasting and free of estrogen-mimicking chemicals commonly found in plastics, like bisphenol-A (BPA). Silicone is a synthetic polymer made from the Earth's element silicon, which is the second most abundant element in the earth's crust and makes up about 27% of the average rock. When mixed with oxygen, silicon becomes silica and is present in nature as sand and quartz that are commonly used in making glass. Non-toxic and rubber-like, the silicone material used in our products is much more durable and longer lasting than plastic and it does not contain petroleum. Silicone resists degradation resulting from prolonged use as well as exposure to extreme temperatures and can safely be put in the dishwasher or the oven. Although silicone is not biodegradeable, scientists believe the material is not hazardous to the environment nor toxic to aquatic or soil organisms.