Waste is unwanted or unused material produced by human or industrial activities. High-Density Polyethylene (HDPE) is a type of plastic considered safe for use. Polypropylene (PP) is a recyclable thermoplastic with potential as a matrix in particle board composites. The specimen was tested using tensile testing, as well as macro and microstructure analysis. The highest tensile strength was found in the 100% HDPE composition, reaching 23.642 MPa. The highest tensile strength from mixing the three materials was in the specimen with a composition of 60% HDPE, 30% PP, and 10% cassava pulp, with a value of 16.026 MPa. The lowest strength was observed in the composition of 60% PP, 35% HDPE, and 5% cassava pulp, at 4.420 MPa. The increasing proportion of HDPE significantly improves material strength due to its strong and tough mechanical properties, while excessive cassava pulp reduces strength. Macro testing revealed air cavities in the middle of the specimen. Micro testing showed that HDPE and PP do not mix homogeneously, and cassava pulp tends to mix more with PP.