The transport of H 2, He, CO 2, O 2, CH 4, and N 2 at three temperatures up to 65 C was measured in dense, thick composite films formed by amorphous Polysulfone (PSf) and particles of the size-selective zeolitic imidazolate framework 8 (ZIF-8) at loadings up to 16 wt%. The morphological and structural properties of the membranes were analyzed via SEM and density measurement. The addition of ZIF-8 to PSf enhances the H 2 and He permeabilities up to 480% with respect to the pure polymer, while the ideal H 2/CO 2 and He/CO 2 selectivities of MMMs reach values up to 30–40% higher than those of pure PSf. The relative permeability and diffusivity enhancements are higher than those obtained in other polymers, such as PPO, with the same amount of filler. The Maxwell–Wagner–Sillars model is able to represent the MMM H 2/CO 2 separation performance for filler volume fractions below 10%. View Full-Text