In this article, numerical simulations are used to compare polymer-electrolyte fuel cells (PEFCs) with porous flow-field plates to cells with conventional solid plates. The model clarifies the role of the porous plates in humidifying dry reactant streams and managing liquid water. The influence of gas-diffusion-layer (GDL) and bipolar-plate properties and coolant vacuum on the behavior of the cell is investigated. (C) 2007 Elsevier B.V. All rights reserved.