Nanofiber composite proton-exchange membranes composed of Nafion and polyphenylsulfone (PPSU) were fabricated by simultaneously electrospinning Nafion and PPSU into a dual-fiber mat and then processing the mat into a dense and defect-free membrane. Three post-electrospinning processing steps, i.e., interfiber void-filling, Nafion annealing, and acid/water washing were examined to determine their effect on membrane properties. All the dense composite membranes had excellent water swelling and mechanical performance combined with reasonable proton conductivity. Furthermore, this study demonstrates that composite electrospun membranes can be prepared in as little as 16 min, a > 15-fold reduction in processing time relative to previously described electrospun membrane fabrication techniques. (C) 2013 Elsevier B.V. All rights reserved.