Today, humidity sensors have become an integral part of ourdaily lives. In particular, humidity sensors using an electronic measuring principle have become the standard. Although these sensors have proven to be a stable measurement method, they have some disadvantages, such as their long response time or the danger of using them in explosive environments. This paper introduces photonic crystals as an alternative optical measurement approach. Wecombined the novel technology of ultra-fast two-photon polymerisation printing with a thin-film deposition process, namely iCVD. This allowed us to print large area high-precision 3D templates, which weresubsequently coated with a humidity responsive hydrogel thin film (pHEMA) of 20nm. Wewere also able to push the limits of 2PP technology and still produce stable and periodic large-area 3D structures. The flexible customization of hydrogels for ambient conditions make them exceptionally promising for a wide range of sensing applications. Additionally, optical methods for measuring humidity seem to be an excellent alternative to overcome the limitations for current state of the art humidity sensors. The optical detection of changes in ambient air humidity wasachieved by observing color changes of the printed structure within the visible wavelength range. This article is protected by copyright. All rights reserved.