This study addresses the issue of using recycled materials to obtain low-cost structural products for practical applications. Through the use and re-extrusion of virgin high-density polyethylene (HDPE), the effects of the degradation level of HDPE as a matrix phase on its mechanical properties and the mechanical performance of composites produced with the degraded polyethylene have been examined. The degradation level of HDPE caused by reextrusion has been evaluated by the measurement of the melt flow index and mechanical properties of virgin and degraded HDPEs. The results indicate that the modulus and strength of HDPE significantly increase with the addition of polypropylene filled with 30 wt % glass fiber [PP-GF(30)] without any other compatibilizer. However, the final properties of composites with specified glass-fiber contents are dependent on the degradation level of the matrix phase. In addition, the role of ground tire rubber (GTR) in HDPE/PP-GF(30) systems has been examined by the preparation of composites with various GTR contents without any treatments. The results show that the presence of GTR in the final product results in lower stiffness because of its role as a soft filler, but the elongation of the product increases slightly. Furthermore, GTR does not produce any improvement in the impact properties, probably because of the low interfacial adhesion with the matrix phase; therefore, its content should be kept low in the final composition. (c) 2006 Wiley Periodicals, Inc.