In this study, water transport and thermal profile in the through-plane direction of a proton exchange membrane fuel cell (PEMFC) gas diffusion layer (GDL) are reported. Direct optical and infrared access to both cathode and anode GDLs are provided in a typical 50 cm(2) test section. Dynamic visualization (pixel resolution of similar to 0.6 mu m at 28 Hz) of liquid water transport and emergence in the gas distribution channels and diffusion layers are reported and the underlying transport processes are discussed. The temperature distributions across the anode and cathode GDL are also measured with a high resolution infrared camera with a pixel resolution of 5 mu m at 30 Hz. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3560163] All rights reserved.