The incorporation of highly porous activated carbon (aC) to Nafion membranes confers unprecedented levels of water uptake (4 times higher for 10 wt% aC compared to neat Nafion) at a minimal dimensional swelling and results in dramatic enhancements in ionic conductivity at low relative humidity. This behavior reveals the development of a robust network of water nanochannels formed by the carbon pores and the polymeric ionic domains which are structurally stabilized by the rigid Nafion backbone and the non-deformable aC particles. (c) 2012 Elsevier Ltd. All rights reserved.