In this study, novel membranes are designed and fabricated using CTA as the main matrix with contributions of PEG and as-synthesized ZIF-8 nanoparticles. Gas permeation properties of blend membranes containing 25-45 wt.% PEG and MMM5 containing 2-20 wt.% ZIF-8 crystals are evaluated for the separation of He from N-2 and CH4 at various temperatures and pressures. The properties of synthesized ZIF-8 nanoparticles as well as membranes are well characterized. Among all the prepared membranes, the MMMs membrane with composition of CTA/PEG/ZIF-8 (60/20/20 wt.%) exhibits the best performance (P-H2 = 73.25 Barrer) for He/N-2 (alpha=43) and He/CH4 (alpha = 40) separations. In addition, various predictive permeation models are investigated in order to gain more insights about the systems and for validation of the experimental results. The %AAREs of the models are high, while the best value is obtained by applying the Maxwell model (5.98). Also, by choosing Lewis-Nielsen model and taking into account some of the non-ideal effects such as particle pore blockage, polymer chains rigidification as well as the effect of particles size on the rigidified layer thickness, a new while accurate model is proposed. Finally, the accuracy of the newly developed model is examined utilizing several experimental data. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.