Diffusion of water in a glassy epoxy resin has been studied by the sorption method. Film thickness scaling is used as a diagnostic tool for non-Fickian sorption processes. A sorptiondesorption cycle effectively increases the preexisting free volume in the resin and renders the subsequent sorption process different from the original. The effect is understood by considering the time scale for diffusion and that for molecular relaxation of the glassy polymer network. A non-Fickian sorption process is observed for an insufficiently cured resin and is caused by the resin undergoing further postcuring in the sorption process. It is shown that oxidation of the resin during sorption also gives rise to non-Fickian processes previously described in the literature as diffusion anomalies for epoxies. It is further shown that the difference between sorption and resorption curves is not caused by irreversible damage to the resin but due to reversible changes in network conformations.