Flatness-dependent thermal conductivity of graphene-based composites

► We develop a novel model for the thermal conductivity (TC) of graphene composites. ► We adopt a new concept, flatness ratio, into the theoretical model. ► TC predictions show a good agreement with reported experimental data. ► Flatness ratio acts as a dominant role in determining the effect of other factors. ► 2D geometry is the main factor for graphenes outperforming CNTs in TC enhancement.