In this work, we investigated the influence of nano-particle orientation in polymer electrolyte membrane (PEM) fuel cell microporous layer (MPLs) on heat transfer behavior. In practical applications, polytetrafluoroethylene (PTFE) is added as binding and hydrophobic agents to the MPL. However, the thermal conductivity of PTFE is significantly lower than that of carbon, and the impact of PTFE content on the thermal conductivity of the MPL has not been reported. In this work, we considered a phase-differentiated model with carbon, PTFE, and air as separate phases, and heat transfer was modeled through the nano-particles using Fourier's law of heat conduction. Particle separation was found to have the strongest impact on the thermal conductivity of the MPL. The thermal conductivity decreased by over 50% when the particles were separated by 10 nm. The thermal conductivity was not largely impacted by particle radii, but the thermal conductivity increased by 8% when the PTFE filling radius increased from 10 nm to 30 nm. The same methodology was also used to calculate the electrical conductivity of the MPL. The increase in particle separation resulted in a linear decrease in the electrical conductivity, with a decrease of 16.4% when the particle separation increased from 0 nm to 10 nm. Introducing a fluid phase has an insignificant effect (less than 1%) on the electrical conductivity, and the impact of changing the filling radii was also significantly less than for the case of thermal conductivity. (C) 2015 Elsevier Ltd. All rights reserved.