Thermally conductive and electrically insulating polymer composites are in great demand for the heat management of modern electronics. Herein, a novel method consisting of the foaming and subsequent infiltrating processes is developed to construct a thermally conductive 3D framework in silicone rubber (SR) for enhancing the thermal conductivity. The thermal conductivity of an alumina (Al2O3)/SR composite with a 3D framework (3D-Al2O3/SR) reaches 0.747 W/(m K) at 32.6 wt% Al2O3 loading, much higher than that of the corresponding Al2O3/SR composite with randomly dispersed Al2O3. This difference can be attributed to the effective thermally conductive 3D network fabricated by foaming and the strong interfacial adhesion between the framework and SR matrix. The volume electrical resistivity of the 3D-Al2O3/SR composite at 32.6 wt% Al2O3 loading is 2.12 x 10(14) omega cm, indicating its good electrical insulation. This method is facile, versatile and of low cost, which could pave the way for designing and preparing high-performance polymer composites used for heat dissipation.