Moving beyond the conventional understanding of solar energy as a power source, this presentation will discuss the constituents of solar energies and their capacity to act as an agential material, i.e. one that interacts, mediates, and facilitates change in smart textile designs. The concept of agential materiality suggests that phenomena such as solar energies are not passive forces but are active participants in the co-constitution of natural and designed environments. Solar energies comprise sunlight and its constituents: visible light (through which we experience illumination and colour), ultraviolet (UV) wavelengths, and infrared wavelengths. These each contain inherent variabilities in their qualities, expressions, intensities and temporal patterns that can directly influence textile material properties and the interactive and responsive aspects of smart textile design. This perspective draws from a ‘more-than-human design’ theoretical framework, which argues for the recognition of non-human actors in the design process. Through this lens, solar energies inform the properties, behaviours, and expressions of textile design materials and challenge conventional hierarchies between the animate and the inanimate.