A pore level model of the vapor transport, heat transfer, and evaporation are incorporated into a network model to study the mass transport inside a porous transport layer of proton exchange membrane (PEM) fuel cell. Viscous models are used for the flow of liquid water and for the air-vapor mixture. Thermal transport is included by performing an energy balance at each pore. Existing models for vapor transport and evaporation are adapted for incorporation into the network model. The effect on the water transport of different gas channel conditions such as temperature and relative humidity is studied. Effective thermal conductivities and vapor diffusivities are calculated from the simulation and compared against published values. (C) 2013 Elsevier Ltd. All rights reserved.