One of the main properties to be satisfied in hydrogen applications is low gas permeability. In composite materials, this property depends on the processing parameters and in particular on the residual porosity, but also on the quality of the fiber/matrix interface. This is particularly the case in composites involving a thermoplastic matrix with carbon fibers as the lack of reactive group on the fiber surface can limit the level of interfacial interaction between the reinforcement and the matrix. In this study, the role of the interface is therefore analyzed through the investigation of the hydrogen permeability of CF/PVDF and CF/PPS composites manufactured with different grades of polymers and reinforcements. The hydrogen permeability of the composites was determined, and a correlation with the crystallization behavior of the matrix on the fiber surface could be identified. Hydrogen permeation decreases when the fiber favors matrix nucleation.