Both in-plane and out-of-plane directions exhibit anisotropic thermal conductivity due to the orientation of the BNNS filler. Oriented fillers form a thermal conduction path along the inplane direction, resulting in a higher in-plane thermal conductivity than the out-of-plane thermal conductivity. It is observed that the thermal conductivities of all the composites measured increases along with the filler loadings. The thermal conductivities of the neat unfilled epoxies LY564 and LY5052 are 0.27 Wm -1 K -1 and 0.2 Wm -1 K -1 respectively. With 1 wt% BNNT incorporated into the 30 wt% BNNS filled epoxy composites possesses a thermal conductivity of 2.6 Wm -1 K -1 and 3.4 Wm -1 K -1 , i.e. a 10 to 17 fold increase in comparison to the pristine epoxy (Figure ). The increased thermal conductivity in (BNNT-BNNS)/epoxy composites is due to two factors; (1) higher thermal conductivity of BNNSs (these can more effectively improve the thermal conductivity of the composite), and (2) BNNTs/BNNSs hybrid nanofillers are uniformly dispersed in the epoxy matrix which helps the synergistic improvement of BNNTs/BNNSs hybrids on the thermal transport properties.