The use of wastes in the development of useful material is a key aspect of solid waste management. The aim of this study was to utilize biochar from elephant grass ( Pennisetum purpureum) as fillers in polystyrene composites with focus on the morphological and thermal properties of the developed composites. The composites were prepared by hand lay-up technique. The prepared resin and final composite were characterized using scanning electron microscopy, differential scanning calorimetry and Fourier-transform infrared spectroscopy. The biochar also did not contain any reactive hydrophilic groups, thus, it is compatible with polystyrene. Estimated heat capacities of the composites from the thermal test results showed that to obtain a composite of heat capacity range between 600 J/kg·K and 760 J/kg·K, a 10–30 wt% range of biochar composition should be maintained. At 30 wt% biochar composition, heat capacity was at a maximum value of 757.66 J/kg·K.