Recycled high-density polyethylene (HDPE) was incorporated with graphene nanoflakes in a solvent at different concentrations (0, 1, 2, 4, and 8 wt%), and then the mechanical, thermal, electrical, and surface hydrophobic properties of the resultant nanocomposites were determined using universal tensile testing, thermal comparative, capacitance bridge, and goniometer techniques, respectively. The test results revealed that the mechanical, thermal, and dielectric properties of the polymer matrix nanocomposites were increased as a function of graphene concentrations, whereas the surface hydrophobic values were slightly increased at lower concentrations and then reduced at higher concentrations. These improvements occur mainly because of the excellent properties of graphene nanoflakes, such as tensile strength (150 GPa), Young's modulus (1.0 TPa), thermal conductivity (4,840-5,300 W/m K), electrical conductivity (1.3 3 10 6 S/cm), electrical current density (10 13 A/cm 2 ), surface hydrophobicity (>120 ), and surface smoothness/roughness (<1 nm). The worldwide consumption of polymeric products has been drastically growing, and consequently polymeric waste materials have been rising up, as well. Although the plastic recycling and reprocessing rates are considerably high, physical properties and economical values of the recycled plastics are significantly low, limiting the reuse of recycled plastics in many industrial applications. As a result, this study provides a detailed explanation of how to improve recycled plastics into highly valued new products for applications in various industries, such as transportation, energy, electronic, construction, and so forth. POLYM. COMPOS., 36:1565-1573