Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations with Teflon AF2400 and Teflon AF1600 predicted diffusivities and solubilities of He and N-2 that corresponded reasonably with available experimental data. The results of the MD simulations further showed that NF3 had a higher diffusivity than CF4 in both polymers and that the NF3/CF4 diffusion selectivity was 67% higher in Teflon AF1600 compared to Teflon AF200. However, because the GCMC simulations failed to offer a conclusive answer to the role of the solubility selectivity w.r.t. NF3 and CF4, the non-equilibrium lattice fluid (NELF) model was used to further evaluate this aspect. Consequently, the combined NF3/CF4 diffusion and solubility selectivity values predicted permeability selectivities that corresponded well with the previously reported experimental data, which confirmed that a lower FTV resulted in an increased NF3/CF4 solubility and diffusion selectivity. (C) 2014 Elsevier B.V. All rights reserved.