Since the bridging interactions between BNNTs and BNNSs can lead to the formation a highly efficient 3D network that can form rather easily a path for the heat flow through the composites. 20 To better understand the improvement in thermal conductivity we analysed the structure of the composites to relate the performance to the distribution and alignment of the fillers. It was observed from the SEM images shown in Figure -e, as well as the combined schematic illustration in Figure , that most BNNTs are located in between BNNSs, which significantly increases the amount of contact area. This is because the contact geometry changes from a 2D point contact to a 1D linear contact compared to individual BNNSs and BNNTs nanofillers.