The exploration and evaluation of new composites possessing both processability and enhanced hydrogen storage capacity are of significant interest for onboard hydrogen storage systems and fuel cell based electric vehicle development. Here we demonstrate the fabrication of composite membranes with sufficient mechanical properties for enhanced hydrogen storage that are based on a polymer of intrinsic microporosity (PIM-1) matrix containing nano-sized fillers: activated carbon (AX21) or metal–organic framework (MIL-101). This is one of the first comparative studies of different composite systems for hydrogen storage and, in addition, the first detailed evaluation of the diffusion kinetics of hydrogen in polymer-based nanoporous composites. The composite films were characterised by surface area and porosity analysis, hydrogen adsorption measurements, mechanical testing and gas adsorption modelling. The PIM-1/AX21 composite with 60 wt% AX21 provides enhanced hydrogen adsorption kinetics and a total hydrogen storage capacity of up to 9.35 wt% at 77 K; this is superior to the US Department of Energy hydrogen storage target. Tensile testing indicates that the ultimate stress and strain of PIM-1/AX21 are higher than those of the MIL-101 or PAF-1 containing composites, and are sufficient for use in hydrogen storage tanks. The data presented provides new insights into both the design and characterisation methods of polymer-based composite membranes. Our nanoporous polymer-based composites offer advantages over powders in terms of safety, handling and practical manufacturing, with potential for hydrogen storage applications either as means of increasing storage or decreasing operating pressures in high-pressure hydrogen storage tanks.