The morphology and microstructure of the materials were studied using field emission scanning electron microscopy (FESEM) on a TESCAN MIRA3. The loading of fillers and thermal stability of the composites was determined through thermogravimetric analysis (TGA), using a simultaneous thermal analyser (STA 449 F5 NETZSCH, Germany) in a nitrogen atmosphere with a heating rate of 10 C/min. Thermal conductivity (k) was calculated using the equation k = D.Cp.d, where D is the thermal diffusivity measured by laser flash apparatus (NETZSCH, LFA 427) for the through-plane direction and a home-made IR thermoreflectance instrument for the in-plane direction. Cp is the specific heat capacity determined by a differential scanning calorimeter (DSC Q100, TA Instruments) with a heating rate of 3 °C/min under a nitrogen atmosphere, and d is the density which was determined by the Archimedes method. The relative densities of all samples were greater than 99% and the uncertainties in Cp and D were 2% and 5% respectively.