In this work, a new method to estimate the thermal conductivity of polymer composite was suggested. For this purpose, polymer composites composed of high‐density polyethylene (HDPE) and boron nitride (BN) were prepared by twin‐screw extruder melt‐mixing, followed by compression molding technique, and their microstructure was investigated by material simulation. Consequently, the Cf parameter of Agari and Uno equation, which represents an ease in forming conductive chains, was quantified by “Structure factor (related with conductive pathway)” and “Interfacial factors (related with thermal resistance)”, ultimately helping us evaluate the thermal conductivity of arbitrary composite system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013