The reason is mainly due to phonon scattering caused by defects interfaces etc and the difficulty of pro￾cessing due to excessive addition of thermally conductive fillers By adding hybrid thermally

). These hybrid fillers have different shapes, sizes, and compositions, and have different roles in improving the thermal conductivity of polymer composites. For example, SiCw/SiCp binary hybrids can enhance the thermal conductivity of epoxy composites by forming a percolation network and reducing the phonon scattering caused by the SiCp particles [192]. MWCNT/Al2O3 binary hybrids can improve the thermal conductivity of polyethylene composites by increasing the interfacial thermal conductance between MWCNT and Al2O3 particles [193]. Ag/graphene binary hybrids can enhance the thermal conductivity of epoxy composites by forming a three-dimensional thermal conductive network and reducing the thermal resistance at the interfaces between Ag and graphene [127]. BN/GNPs/CF multi-hybrids can improve the thermal conductivity of epoxy composites by increasing the thermal conductivity of the polymer matrix, forming a percolation network, and reducing the phonon scattering caused by the BN and GNPs particles [198].

In summary, the addition of hybrid thermally conductive fillers into polymer matrix can effectively enhance the thermal conductivity of polymer composites, and the choice of hybrid fillers should be based on the specific application and requirements of the composites