In this work, reground post consumer plastic waste was melt blended with reinforcing additives and processed into boards using an extrusion molding process. The additives used were glass fiber, 50% long glass fiber reinforced polypropylene pellets, and polypropylene. Compressive, flexural and nail pullout tests were performed on the extruded plastic composite lumber substitute materials at three temperatures, namely -20°C, 20°C and 50°C. Similar tests were also performed on pressure treated lumber for comparison. In addition, the coefficient of friction of each formulation was evaluated both wet and dry.The results of the study show that additives and fibrous reinforcements can bring the compressive and flexural properties of the commingled plastic waste lumber closer to those of pressure treated lumber.