Composites of low-density polyethylene (LDPE) containing 1 wt% and 5 wt% polyhedral oligomeric silsesquioxanes (POSS) of different substituents (methyl, isobutyl, isooctyl) were obtained by extrusion. The composites' potential application in high-voltage (HV) power cable insulation was investigated by broadband dielectric spectroscopy, progressive-stress breakdown tests, and surface partial discharge tests. Thermal conductivity and viscoelastic characteristic were also examined as they play an important role in both material property and manufacture. Additional measurements using scanning electron microscopy and differential scanning calorimetry were carried out to obtain information for possible performance explanations. The results showed that POSS could enhance the erosion resistance and slightly improve the thermal conductivity of LDPE without compromising its dielectric breakdown strength or unfavorably increasing its dielectric permittivity or viscosity. (C) 2017 Elsevier Ltd. All rights reserved.