Hybrid filler with proper filler ratio can better improve the thermal conductivity of polymer composites than the single filler. However

there is a lack of an effective thermal conductive equation of the hybrid filled composites. In this paper

a two-step analytical model was developed for calculating the effective thermal conductivity of composites containing hybrid single-walled carbon nanotubes (SWCNTs) and graphite nanoplatelets (GNPs) filler. Based on the experimental observation in the literature

a unit cell containing a "bridging connection" structure was abstracted

and thermal resistance method and Maxwell-Garnett effective medium approach were used to derive the model with the assumption that the unit cell is an equivalent uniform matrix and the non-bridging SWCNTs is the filler. By order of magnitude analysis

the thermal conductive equation was simplified. The modeling results were highly consistent with the experiment results in the literature. When the total mass fraction of hybrid fillers is constant

the effective thermal conductivity of composites firstly climbs up and then declines with the increase of GNPs

showing a clear synergistic effect. At a certain mass fraction ratio of hybrid filler

the effective thermal conductivity of composites rises with the increase of mass fraction of hybrid fillers.