Synthetic and natural smectite clays, with different structural and physical parameters, were tested as nanofillers for the creation of Nafion nanocomposites. The solution intercalation method has been successfully applied for incorporation of layered materials into the polymer, while the effect of the solvent, temperature and filler loading were examined in order to determine the optimum conditions for the preparation of highly homogeneous composites.NMR methods, including pulsed-field-gradient spin-echo (PFGSE) and spin-lattice relaxation time (T1) were used to investigate behavior of water confined in recast Nafion and in Nafion–clay hybrids membranes.The transport mechanism appears to be influenced from the dimensions of the dispersed platelets and mainly from the type of nanocomposites formed upon mixing the clay particles with the polymer matrix. Compared to pure Nafion, the water uptake and the water diffusion of the hybrid membranes are increased, with the exception of the Kunipia-Nafion composite. A remarkable behaviour at high temperature is observed, where composite membranes maintain stable and unwavering diffusion for many hours and in conditions of not humidification, proving the exceptional water retention property of these materials. Finally the hybrid membranes are much stiffer and can withstand higher temperatures compared to pure Nafion, hence both these characteristics are highly desirable for use in fuel cell applications.