At present proton exchange membrane (PEM) performance levels and fuel cell stack operating conditions, require a plate area specific resistance of less than 30 m ohm cm(2) and a plate thickness of less than 2 turn are required to meet the vehicular volumetric power density target (> 2 kW l(-1)). Unfortunately, it is difficult to meet these targets, and simultaneously obtain good mechanical properties and low through-thickness hydrogen permeation rates when using polymeric plate materials. Polymers are brittle at the high conductive filler concentrations (e.g. > 50 v/o graphite) required for high conductivity, and are more likely to generate high convection-driven H-2 permeation rates at a high graphite loading and at a thin plate thickness. As a result, high scrap rates are realized during plate manufacturing and stacking operations, and excessive permeation rates are anticipated in pressurized stacks. This study addresses H-2 permeation concerns associated with using thin, highly-filled composite plates, and investigates factors affecting permeation such as plate temperature, thickness, graphite loading, and aging. (c) 2005 Elsevier B.V. All rights reserved.