Published experimental and theoretical investigations conducted to estimate the effective diffusivity of the gas diffusion layers (GDLs) and other porous layers in polymer electrolyte fuel cells (PEFCs) have been reviewed. The main observations are that most of the diffusivity investigations were on the Toray carbon papers and that fewer studies have been conducted to estimate the effective diffusivity of the microporous layers (MPLs) and the catalyst layers. The main finding set by most of the reviewed investigations is that the Bruggeman relation significantly overestimates the effective diffusivity of the GDL. In order to evaluate how this overestimation is reflected on the performance of the fuel cell, a numerical study has been conducted. The outputs of this numerical study have shown that the Bruggeman relation significantly overestimates the performance of the fuel cell; this overestimation may be up to a factor of 2 or more. It is therefore recommended that empirical relations are used rather than the Bruggeman relation to calculate the effective diffusivity of the GDL materials. Also, the results suggest that a distinction between the GDL and the MPL in the single-phase modelled fuel cell should be made if the difference between the porosities of the two layers is significant. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.