A 1D non-isothermal model has been developed to study the optimum morphological properties of HT-PEMFC components that will help the catalyst layer retain water vapor generated by the electrochemical reaction and that delivered by the feed gases. The use of a microporous layer (MPL) helps retain water generated in the catalyst layer (CL), and the effectiveness of the MPL in retaining water vapor in the CL increases the MPL pore size and porosity are reduced. Reducing the GDL porosity is found to help retain more water in the CL but the pore sizes and porosity of the PEMFC components should not be too small, so as to avoid increased O-2 concentration overpotentials. The optimum values of MPL and GDL porosity depend on the operating conditions such as the cell voltage, operating pressure, and inlet relative humidity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3569711] All rights reserved.