Generally it is a carbon-based fibrous medium that allows for the transport of electrons through the fibers anddistributes the reactants through the void space to the catalyst layer in a PEM fuel cell. In the present work, amicrostructure study of reactant transport is carried out by reconstructing the typical fibrous microstructureof the GDL and investigating the transport characteristics of the porous medium using computational fluiddynamics (CFD) simulations. The results confirm the applicability of Darcy’s law formulation for permeabilitydetermination and Bruggemann correction for calculation of effective diffusivity for typical conditions encoun-tered in PEM fuel cells. Macroscopic material properties such as through-plane and in-plane permeabilitiesand effective diffusion coefficient are determined and compared against experimental values reported in theliterature.