We investigate the use of stiffness-controlled polydimethylsiloxane (PDMS) endplates with Young's modulus of 7.50 x 10(5) Pa and 8.68 x 10(5) Pa for improving the performance of flexible fuel cells. The maximum power densities of stacks with PDMS endplates with Young's modulus of 7.50 x 10(5) Pa and 8.68 x 10(5) Pa are 82 mWcm(-2) and 117 mWcm(-2), respectively. The flexible fuel cells produce a maximum absolute power of 1.053 W (i.e., the power density is 117 mWcm(2)) under a bending radius of 15 cm. Interestingly, their impedance spectra reveal that the ohmic and faradaic resistances decrease under the bent condition. Furthermore, the decreased resistance and corresponding performance enhancement are due to the increased compressive force normal to the membrane electrode assembly, which is investigated using a finite element method of stress distribution within the flexible fuel cells. As our experiments show, the faradaic impedance decreases significantly because the bending radius decreases from 36 cm to 15 cm. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.