Organically-modified montmorillonite (OMT) is added in the HDPE and PP matrices into which PEG and PPG are used as a compatibilizer to investigate the behavior of thermal conductivity for polymer/clay nanocomposites. The results indicate that the thermal conductivity of all nanocomposites increases with temperature. Clay incorporation also increases the thermal conductivity. HDPE and PP nanocomposites with 5wt% of clay content show the augmentation of 19 and 23% for thermal conductivity at 20°C with respect to their pure polymers. Mathematical modeling of nanocomposite sheets reveals that the addition of clay into the HDPE and PP matrices up to 10wt%, under the current circumstances of this study, and increase in temperature up to 50°C do not significantly affect the temperature distributions.