Sustainability and Circularity are two critical concepts driving economic, industrial, and societal change worldwide, and the electrical infrastructure sector is feeling real pressure to adapt, change and improve. Intensifying urban growth, regulatory changes, effective asset management, the drive for integrating renewable generation and battery storage, bottom line financial pressure, and improving human and environmental conditions, are all factors that influence decisions made by utilities, substation designers and transformer manufacturers. Against this background, there is a growing recognition of the role to be played by modern, ester-based transformer insulating liquids. Synthetic and Natural esters have become an established alternative that enable cost and carbon savings in substation designs due to being less flammable and readily biodegradable, while also delivering operational flexibility and the potential to extend asset life. But there are important distinctions to be made, and questions to be asked, about the ester liquid landscape, not least about what happens at end of use? This presentation will answer such questions and more, while clearly delineating a case for embedding newly developed MIDEL ester liquids as a key element in delivering a truly sustainable and safer future for people and the places where they live.