The advantages that plastic‐based composites provide over epoxy‐based composites have catalyzed interest in the former in recent years. Polystyrene, a common packaging plastic, has been used for the production of composites. However, its hydrophilicity and curing duration are issues that undermine its commercialization. In this study, two fillers, calcined cow bone and kaolin, were introduced into a polystyrene resin matrix in varying concentrations through the hand lay‐up method. The composites were thermally cured at a temperature of 200°C for 3 h, after which they were characterized for their thermal and microstructural properties. DSC analysis revealed that the presence of kaolin improved the thermal property of the composite more than cow bone. The FTIR results revealed that the filler(s) were incorporated into the matrix via chemical reactions, as evidenced by bond breakage and formation. EDX results confirmed the incorporation of the fillers, with carbon being the most dominant element in the composites. It showed that the cow bone introduced elements such as phosphorus and calcium, while the kaolin introduced elements such as silicon and aluminum to the composite. SEM micrographs showed the presence of good interfacial adhesion between the filler(s) and the matrix. This study has shown that thermal curing is a viable solution to the shortcomings of polystyrene‐based composites and their commercialization.