The significance of this product is far reaching as it takes petroleum completely out of the equation. That's because Greenware is made entirely of corn. The cups and lids are thermoformed out of Nature Works polylactic acid, a polymer derived from corn starches. Polylactic acid is produced by isolating the starch stored in corn kernels, which is then stored into sugars. During a process of fermentation and separation, the sugars become lactic acid, which is used to create the plastic polylactide.