The performance and water management characteristics of polymer-electrolyte fuel cells depend upon the heat and mass transport properties of the components. The influences of the thermal conductivity and thickness of the cathode gas-diffusion layer on the ability to operate stably over a range of temperatures and relative humidities are investigated in this paper. Low thermal resistance is detrimental at low temperature and beneficial at high temperature. The opposite trends hold for mass transport, although the voltage losses associated with oxygen concentration polarization diminish the benefits of increasing the resistance to mass transport. (C) 2013 Elsevier B.V. All rights reserved.