The lipid bilayer is an impermeable barrier that controls and regulates on either side of the membrane the surrounding liquid environment composition. The importance of such mechanism is vital and understanding of such passive transport is the scope of this proposal. Here we are interested in studying the membrane permeability to water using time resolved SANS coupled with contrast variation. The principle is to follow the scattered intensity of a hydrogentated vesicle solution when diluted with D2O. To follow water permeation, data will be taken using the stop flow in second time frames in order to catch the fast kinetics. The resulting changes in scattering would be a result of the intake of the vesicle (determined by a shift in the scattering curve corresponding to a transition from a core shell object to a single shell scattering). The behavior of water permeation as well as its kinetics and energetics with different lipid bilayer will be investigated as a function of membrane curvature and temperature. Such a study will clarify the mechanism of permeation and its Arrhenius activation energy as well as the effect of membrane lipid organization and fluidity.