The properties of perfluorosulfonic acid ionomers (PFSIs) such as DuPont's Nafion (R) have been extensively characterized during the last decades. However, despite its importance for the upcoming industrialization of PFSI-based products no detailed investigation of the welding behavior of PFSIs has been performed. This paper investigates the welding behavior of Nafion (R) NRE-211 membranes common in both academia and industry over an industrially relevant parameter range of time, temperature and pressure. The strength evolution of the welded interface shows a linear dependence with square root of time and an Arrhenius temperature dependence. It is thus suggested that the welding behavior of Nafion (R) membranes can be predicted by the reptation model from polymer dynamics. Time-temperature master curves for a large range of parameters are constructed. Pressure is shown to have positive effects at very low welding times, but strongly negative effects at longer welding times, which can be explained by the model. Welding time and final strength of the fully healed interface are predicted using measurement and literature data. A short discussion on thermal transitions and on the role of crystallinity is also presented. (C) 2014 Elsevier B.V. All rights reserved.