Mechanical properties and thermal conductivity of epoxy composites reinforced with recycled clamshell container waste as a micro filler (RCCF) were studied. The studies have been carried out to identify the influence of the two variables, the heating time periods (HT) within the range of 2, 4, 6 min., and wt % within the range of 1 %, 2 %, 4 % of recycled clamshell container waste that has been used as a reinforcing filler of epoxy composites. Recycling polyurethane waste aims to control and maintain a pollution-free environment, which is currently considered a difficult issue in addition to achieving low-cost aspects in preparing the composites. According to the method of no-combustion heating, the clamshell waste was converted from the natural plastic state into solids that were later made into 75 μm micro filler by grinding. Composites were ranked using grey relational analysis (GRA). The effect of each control parameter on response variables was analyzed by the Taguchi method. Using MINITAB 19 software, regression equations were obtained for each variable of mechanical properties and thermal conductivity to predict the properties of epoxy composites. The results of the addition of recycled clamshell container waste to epoxy resin show an improvement in the mechanical properties and thermal conductivity of the composites. The optimal value of the two factors was at HT2wt2, i.e. HT and wt % of 4 min and 2 %, respectively. The optimization values for the bending strength, impact strength, tensile strength, stiffness and thermal conductivity are 68.2 MPa, 10.348 kJ/m2, 21.08 MPa, 80 Shore D and 0.504 W/m·C°, respectively. The proposed Taguchi methodology based on grey relational analysis has been shown to be effective in solving multi-feature decision-making problems.