High-flux nanoporous single-layer graphene membranes are highly promising for energy-efficient gas separation. Herein, in the context of carbon capture, a remarkable enhancement in the CO 2 selectivity is demonstrated by uniquely masking nanoporous single-layer graphene with polymer with intrinsic microporosity (PIM-1). In the process, a major bottleneck of the state-of-theart pore-incorporation techniques in graphene has been overcome, where in addition to the molecular sieving nanopores, larger nonselective nanopores are also incorporated, which so far, has restricted the realization of CO 2sieving from graphene membranes. Overall, much higher CO 2 /N 2 selectivity (33) is achieved from the composite film than that from the standalone nanoporous graphene (NG) (10) and the PIM-1 membranes (15), crossing the selectivity target (20) for postcombustion carbon capture. The selectivity enhancement is explained by an analytical gas transport model for NG, which shows that the transport of the stronger-adsorbing CO 2 is dominated by the adsorbed phase transport pathway whereas the transport of N 2 benefits significantly from the direct gas-phase transport pathway. Further, slow positron annihilation Doppler broadening spectroscopy reveals that the interactions with graphene reduce the free volume of interfacial PIM-1 chains which is expected to contribute to the selectivity. Overall, this approach brings graphene membrane a step closer to industrial deployment.