This paper reviews the characterization of the base strength and impact of water absorption on biodegradable, namely, soy protein-based plastics prepared by different methods. The initial approach included using different quantities of soy hydrolysate plasticized with glycerol, which is widely known for its plasticizing effect. With the second approach, the raw polymer was which plasticized with glycerol compounded with different additives such as polycaprolactone or zinc sterate, and was also heat-treated at various temperatures after injection molding. The results indicated the polycaprolactone and, respectively, a medium to high heat treatment significantly enhanced tensile strength and greatly decreased water absorption. The soy hydrolysate formulations that were studied enhanced tensile strength but didn not significantly improve elongation or water absorption.