Celtec-V is a proton exchange membrane based on polybenzimidazole (PBI) comprising an interpenetrating network of polyvinylphosphonic acid designed for application in the direct methanol fuel cell. The properties and fuel cell performance of Celtec-V are investigated and compared against a Nafion 117 standard. It is shown that with the PBI-based membrane, fuel cell performance can be sustained to higher methanol feed concentration at around half the methanol crossover rate. Above 1.0 M methanol, Celtec-V outperforms Nafion 117. Furthermore, lower water permeation is observed, with Celtec-V having an electro-osmotic drag coefficient of around 1 compared to a value of 4-5 for Nafion 117. Room for improvement is identified in the ohmic resistance of the membrane and the cathode-membrane interface, where higher losses are observed at increasing current density. (C) 2007 The Electrochemical Society.