<p>Particles with high thermal conductivity exhibiting a bimodal size distribution can significantly improve the effective thermal conductivity (ETC) of particle filled three-phase composites (TPCs). Traditionally, the primary thermal conductive mechanisms have been elucidated through the concept of packing density, as established in granular powder mechanics for hybrid granular mixtures with binary size distributions. However, this conventional packing density is inapplicable to the <i>sb</i>-TPCs that are prepared by solution blending and mold casting, where porosity reduction is absent. To date, a micromechanics-based model specifically addressing this phenomenon remains undeveloped. Given that the matrix phase possesses low thermal conductivity, the matrix regions distant from high TC fillers are analogous to air voids in granular materials, and thus termed <i>ineffective</i> matrix. According to packing theory, the utilization of a binary size distribution effectively reduces the concentration of the <i>ineffective</i> matrix. Based on this concept, the interpolated double inclusion model was firstly employed to construct a fictitious inclusion comprising the particle and its surrounding matrix. The Chang-Deng model was then applied to quantify the concentration of the <i>ineffective</i> matrix in the <i>sb</i>-TPC, and finally the Zehner, Bauer and Schlunder (ZBS) model was adopted to predict their ETCs. The predictions were validated against relevant experiments to assess the validity of the developed model. Additionally, parametric analyses were performed to elucidate the effect of various factors on model performance. The developed micromechanics model presents potential as an effective tool for designing of <i>sb</i>-TPCs with elevated ETCs.</p>