In this work, the through-plane porosity distributions of paper and felt gas diffusion layers (GDLs) treated with micro-porous layers (MPLs) are measured using microscale computed tomography. The porosity distributions of the GDL microstructure and cracked MPL coating are analyzed and presented independently. In the MPL core region, the porosity of the cracked MPL is found to steadily decrease towards the catalyst layer side. Through comparison, the extent to which the MPL penetrates the GDL is also observed. From cross-sectional images of the MPL treated GDL, crack locations were found to correspond with adjacent fibre locations, indicating that fibres can influence the presence of cracks in the MPL. We also present the through-plane combined porosity distribution for the GDL and cracked MPL, which can be employed for predictive modelling of liquid water transport in the polymer electrolyte membrane fuel cell (PEMFC). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3594636] All rights reserved.