The DMFT calculations were performed to establish a non-equilibrium steady state flux across the lattice structure. The outcome of the DMFT calculation is the local density and flux on each site, from which other properties can be derived. Eq. 6 is used to calculate the permeability where J, L, and A ′ are the total flux in the direction of pressure gradient, length of the membrane, and crosssectional area of the membrane, respectively. Fig. -2f shows the perm-selectivity calculated using the DMFT. Firstly, for all the cases, the ideal permselectivity is in good agreement with the actual permselectivity calculated from mixtures. This demonstrates the reasonable validity of using single component permeation data to predict the perm-selectivity for mixtures in agreement with many experimental observations, although systems where this assumption does not hold have also been reported. However, the most important observation from Fig. is associated with the differences in the values of permselectivity and sorption selectivity. While the trend is the same for both properties, as selectivity increases with the density of the polymer, the values of perm-selectivity are much lower (as many as two orders of magnitude) compared to sorption selectivity, suggesting that the diffusion is playing a significant role in the fluid separation performance. This is also consistent with the experimental observations, where a large value of S can lead to the so-called "immobilising sorption" effect, where D, and hence the permeability k, are reduced. Using the lattice model, we can elucidate which transport effects contribute to the effective perm-selectivity in disordered structures.