Proton Exchange Membrane Fuel Cell (PEMFC) components are known to deteriorate during use, in time scales much shorter than that required for commercially successful deployment of this technology. Therefore, servicing operations such as identifying and replacing poorly performing components will likely be required to extend the operational lifetime of PEMFC stacks. During such servicing operations fuel cell components are subjected to cyclic compression and expansion due to opening and rebuilding of the fuel cell stack. This cyclic compression may further contribute to the deterioration of PEMFC components. There are several reports in the literature showing the effect of static compression on change in GDL properties, however the present work focuses on the effect of cyclic compression on GDL properties, an aspect that has not been reported in detail elsewhere. This paper focuses on the impact of cyclic compression on the Gas Diffusion Layer (GDL). The results indicate that cyclic compression causes significant and irreversible changes to the structure and properties of the GDL such as surface morphology, surface roughness, pore size, void fraction, thickness, electrical resistance, contact angle, water uptake and in-plane permeability. The implications of these results are considered. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.