Water management has long been recognized as a critical issue in the operation of a Polymer Electrolyte Membrane Fuel Cell (PEMFC). If the membrane is allowed to dehydrate then ionic conductivity will drop and result in significant power losses. At the opposite extreme, if not enough water is removed from the membrane then liquid water will accumulate in the Gas Diffusion Layer (GDL) and block the transport of reactants to the reaction sites. In this work, the dynamics of membrane hydration are analyzed while under the influence of a closed-loop control system. From a controller assessment perspective, the membrane model is unique in that through the plane spacially dependent water accumulation is captured. By combining with an electrochemical model and simple material and energy balances over the solid and fluid materials, the dynamics of the membrane are shown to be strongly influenced by the thermal responses of the solid as well as humidity levels in the gas streams, all of which are a function of the controller utilized. We conclude by illustrating the highly sensitive nature of the system with respect to water diffusivity within the membrane. (C) 2011 Elsevier B.V. All rights reserved.