To achieve the sustainability goals set for the European aviation sector, hydrogen- 1 powered solutions have been and are currently being investigated. Storage solutions are of 2 particular interest, with liquid hydrogen tanks posing numerous challenges with regards 3 to the structural integrity of materials at cryogenic temperatures, as well as safety issues 4 because of the high flammability of hydrogen. In this context and in the scope of Horizon 5 2020 Clean Aviation Joint Undertaking (CAJU) project H2ELIOS, the gas permeability 6 of CFRP materials, two thermosets from two different fiber formats and one additively 7 manufactured thermoplastic, was studied. Investigations were performed after thermal 8 shock to 20K (liquid Hydrogen immersion) as well after uniaxial stress application at 9 77K, to investigate their sensitivity to the ageing conditions. Helium gas permeation was 10 tested at RT and its representativeness to Hydrogen permeation in a range of temperatures 11 is considered in the study. The materials’ permeation behavior was compared to ideal 12 Fickian diffusion, as means of identifying ageing-induced micro cracking and related 13 permeation barrier function degradation. Micro-computed Tomography was utilized to 14 verify the presence of cracks within the thermoplastic material. In summary, it was possible 15 to identify and quantify the effect of ageing conditions in terms of permeation coefficient, 16 as well as correlating manufacturing methods to results, for materials designed for liquid 17 Hydrogen storage in aeronautical applications.