Polymeric membranes have several applications of high technological impact: reverse osmosis, controlled drug delivery and fuel cell stacks, among many others. However, the choice of the most appropriate polymer for a specific application entails exhaustive experimental work, which may be reduced significantly if the chemical structures of polymer and transported molecules are taken into account. From physico-chemical data such as viscosity (for penetrants) and relaxation times (for polymers), free-volume parameters might be estimated, as well as Flory-Huggins interaction coefficients. By combining both theories, diffusivity of molecules through dense polymers may be evaluated, what allows us to predict membrane properties as water uptake, or operation data as equilibrium concentrations for pervaporation and methanol crossover in the case of fuel cell applications. Simulation results are compared with those in the literature and agreement between the sets of data recommends the proposed method as a helpful tool to decide which polymer Is more adequate for a specific purpose.