In this work, the influence of the zeolitic imidazolate framework 78 (ZIF‑78) morphology, with 1D pores, on the mixed matrix membrane (MMM) CO2/N2 mixed gas separation performance is investigated as well as the influence of the feed composition and pressure. Low aspect ratio and a high aspect ratio ZIF‑78 particles are synthesized and incorporated in Matrimid with 10 and 20 wt% additive content. High pressure CO2 and N2 sorption measurements show that both the low and high aspect ratio ZIF‑78 metal–organic frameworks (MOFs) exhibit similar sorption behavior. The incorporation of ZIF‑78 into Matrimid results in improved CO2 permeabilities up to 39%, without compromising the selectivity, relative to native Matrimid membranes. Both at low and high CO2 partial pressures, the MMMs containing the different ZIF‑78 morphologies show equal CO2 permeabilities, indicating that the ZIF‑78 morphology and consequently the aspect ratio are insignificant for these particular MMMs, contradicting previous observations in literature. Thus, depending on the MOF/polymer system, the MOF morphology and aspect ratio can be considered as a design aspect. Finally, a clear influence of feed composition and pressure on the MMM solubility coefficient and diffusivity is observed, emphasizing the importance of the mixed gas composition and measurement conditions.