A set of four Gas Diffusion Layers (GDLs) having different textile properties (i.e. density, warp, weft and weight), produced by an Italian Company (SAATI), and coated with the same Microporous Layer (MPL), was investigated with the aim of assessing the influence of the Gas Diffusion Media (GDM) on the FC performance. Ex-situ compression measurements of the Gas Diffusion Media, i.e. GDL + MPL, were performed. Then, single cell assemblies, mounting the same Catalyst Coated Membrane (Nafion(R) 112; Pt load 0.5/0.5 mg cm(-2)) but different GDM, were tested by means of steady-state polarization measurements combined with Electrochemical Impedance Spectroscopy (EIS). The FC was run under different operating conditions (i.e. humidity and gases flow rate) at constant temperature (60 degrees C): three RHs were selected at the cathode side (i.e. 100, 80 and 60% RH), while keeping constant the RH at the anode side (100% RH). Moreover, all experiments were carried out at constant gas flow rate: for the anode 0.2/0.25 Nl/min (Hydrogen) and for the cathode 1.0/1.6 Nl/min (Air). Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.