A profound understanding of how the degree of deacetylation (DDA), polymerization degree (DP) and photoswitch concentration impact the photomodulation of properties of chitosan(CS)-based responsive materials can serve as a framework for future applications. Herein, we report responsive thin-films manufactured from chitosans with DDA ranging from 70-94% and DP between 170-3380, incorporating 10 30mol% of the light-responsive azobenzene derivative Sodium-4-[(4-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)phenyl)diazenyl]-benzenesulfonate (TEGABS). During UV-irradiation of the 10 30% TEGABS|CS thin-films, e.g. a significant increase of the indentation modulus by 10 ± 5% is observed. UV illumination leads to a decrease of the water vapor permeability (WVP), reducing it by up to 81 ± 17% compared to native state. We demonstrate that TEGABS up to 10% remains as a solid-solution in CS films with differing amount of H-aggregates depending on the DDA and DP. TEGABS in concentrations >10% in CS leads to phase separation of TEGABS crystallites with a diameter of 21 ± 8 nm. To conclude the photothermal heating by UV irradiation and the resulting water evaporation are identified as the primary driving force for the variation in mechanical properties and WVP, with photoisomerization playing a subordinate factor. These findings provide a new pathway for the design of polysaccharide-based water vapor permeable photoresponsive membranes.