PDMS-grafted alumina membranes have already demonstrated high organic solvent permeabilities; described and modeled in this paper are their retention capabilities. In contrast to pure PDMS polymeric membranes, higher retentions were found in nonpolar solvents than in polar solvents. This is attributed to a solvent-induced pore-constriction behavior: confined swelling of PDMS, grafted into the membrane pores, was found to increase retention. To test this hypothesis, pore sizes were obtained by integrating the Ferry, Verniory and steric hindrance pore (SHP) equations into the Spiegler Kedem Katchalsky (SKK) model in order to predict the retention of dyes. Ultimately, a diffusion pore size was introduced into the SKK model to reflect the ability of the solute to diffuse through the swollen PDMS graft. A better understanding of the transport mechanisms that impact performance was achieved by incorporating the unique pore structure of these ceramic-based hybrid membranes into the SKK model.