This study looked at the costs and benefits of producing bioplastics from one of Thailand’s leading crops, cassava. It compares the production of the bioplastic Polylactic acid (PLA) from cassava, with the production of high-density polyethylene (HDPE) from petroleum. It finds that the production of PLA has a net positive benefit for society as a whole. However, it also finds that the efficiency and management of the bioplastic production process must to be significantly improved if PLA is to be a cost-competitive and environmentally preferable alternative to petroleum-based plastics. In light of this, the study makes a number of recommendations as to how the production of PLA could be supported and improved, so that the end product can be both sustainable and cost-competitive.