Thermal and flow properties of perlite-filled high-density polyethylenes (HDPE), studied in the first part of the paper, are discussed. Maximum peak temperatures of endotherms (T-mp) and the corresponding relative peak heights were examined by differential scanning calorimetry (DSC). The data obtained from a Brabender torque rheometer were evaluated to find the melt viscosities at low shear rate during preparation of perlite-HDPE composites. The filler concentration, types of HDPEs, and the use of gamma-APS are found to be effective and influential factors on the thermal and flow properties of these composites.