This presentation focuses on our research on cellulose-based energy-regulating optical materials. Cellulose is highly interesting for optical applications because it is inherently non-absorptive in the visible and can therefore be designed via structure or additives to provide desired reflection, transparency, and coloration. Cellulose further strongly absorbs infrared light in the thermal spectral range around 10 micrometers, making it an effective thermal emitter. This makes cellulose suitable as sustainable material for radiative cooling applications, by which objects are cooled passively by thermal radiation to the cold sky, with zero external energy consumption. I will present our work on cellulose-based radiative cooling,[1], [2] including recent efforts on structurally colored coolers,[3] how to integrate this concept together with solar heating and/or evaporative cooling to power thermoelectrics day and night,[4], [5] and how to achieve electrically tunable cooling systems through combination with electroactive conducting polymers to control the radiative cooling power.[6] The same approach of electrically tuning thermal emissivity of cellulose materials also opens for new types of adaptable camouflage and dynamic anticounterfeiting systems.[7]