Previous studies have explored the relationship between permeability and membrane size. For instance, atomistic simulations conducted by Giro et al. demonstrated that CO 2 permeability is independent of membrane size for membranes thicker than 4 nm. On the other hand, research by Kong and Liu reports a size-dependent permeability for membranes with thicknesses of 6 and 10 nm. Notably, both studies employed identical non-equilibrium MD setups but arrived at different conclusions. To provide some insights, in our previous work, we applied lattice model studies using dynamic mean field theory to investigate this phenomena. Our findings indicate that permeability does depend on the thickness of the membrane for relatively thin membranes. As the thickness of the membrane increases this dependency diminishes and eventually disappears. Our interpretation of this result is as follows. A common assumption in the solution-diffusion theory is that the membrane interfaces on each side of the membrane are in thermodynamic equilibrium with the gas phase.