Experiments conducted on a commercial fuel cell humidifier determined that the water recovery ratio is the best performance metric because it considers the water supplied to the humidifier. Data from a porous polymer membrane with a hydrophilic additive were analyzed under a heat and mass transfer model. The membrane showed low water uptake profiles at relative humidities below 80 percent, and a steep increase in water uptake above threshold. The experiments were conducted with samples of the porous membrane in a single cell humidifier at isothermal conditions at temperatures of 25, 50, and 75 degrees C. The water recovery ratio for the porous membrane decreased with increasing flow rate. The model was verified experimentally and its predictions agreed with the measured data. (C) 2009 Elsevier B.V. All rights reserved.