Compostable Plastics Developed from Sugar-based Polymer Almost 99 percent of plastics are formed from fossil fuels. Our key breakthrough was in finding a way of using a non-food crop to form a polymer, as there are ethical issues around using food sources in this way, said Williams. Current biorenewable plastics use crops such as corn or sugar beet. For the plastic to be useful, it had to be manufactured in large volumes, which was technically challenging. It took three-and-a-half years for us to hit a yield of around 80 percent in a low-energy, low-water-use process, explains Williams.