The diffusion of molecular hydrogen, helium, and neon through a polyvinyl butyral (PVB) membrane is investigated by Molecular Dynamics (MD) simulations. An understanding of the mechanism of this diffusion is crucial to optimize the industrial conditions for the production of PVB with desired properties. In this work, a comparison of the radial distribution functions of light gases (H2, He, and Ne) around the alcoholic- and ketonic-oxygens of PVB shows that H2 interacts more strongly with the membrane than He or Ne. Further, it is found that Ne has a lower self-diffusion coefficient while H2 has more diffusivity through a model of a PVB membrane. Finally, it was found that the mechanism of diffusion of Ne from a low-temperature “hopping” changes to a “liquid-like” mechanism at high temperatures. However, the mechanism of H2 and He diffusion through the membrane was “hopping”/”liquid like” in all studied temperatures.