A permeation process is used as technique to study the viscoelastic properties of three commercial sulfonated polymeric cation-exchange membranes with different morphology. The Zener model was applied to interpret the deformation of the membrane area caused by the application of a hydrostatic pressure difference. The method permits to obtain information about the elastic and anelastic behaviors of the polymer thin film and the retardation time, and to estimate the membrane area change due to its deformation in a liquid medium. The results show that all the investigated membranes have a similar behavior, with a greatest area deformation at lower pressures mainly caused by the time-dependent anelastic strain, although differences are observed depending on the membrane structure. (C) 2014 Elsevier B.V. All rights reserved.