Compression plays an important role in the performance of polymer electrolyte fuel cells (PEFCs). In this study, dynamic compression is applied using a cell compression unit (CCU) to study the effect on performance of a membrane electrode assembly (MEA) with dimension change. The stress/strain characteristics of the MEA are observed to be dominated by the gas diffusion layer (GDL), with the GDL exhibiting a degree of plasticity. Electrochemical impedance spectroscopy (EIS) is used to delineate the effect of compression on contact resistance and mass transfer losses. With increasing compression, a significant reduction in net performance is observed, with the most significant differences occurring in the mass transport regions of the performance curves. As the compression increases, the high-frequency resistance reduces with the improvement in contact resistance between the GDL and bipolar plate material, concurrently the low frequency resistance increases with increasing compression. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.