Motivated and informed by perspectives on sustainability and design, this paper draws on a diverse body of scholarly works related to energy and materiality to articulate a perspective on energy-as-materiality and propose a design approach of materializing energy. Three critical themes are presented: the intangibility of energy, the undifferentiatedness of energy, and the availability of energy. Each theme is developed through combination of critical investigation and design exploration, including the development and deployment of several novel design artifacts: Energy Mementos and The Local Energy Lamp. A framework for interacting with energy-as-materiality is proposed involving collecting, keeping, sharing, and activating energy. A number of additional concepts are also introduced, such as energy attachment, energy engagement, energy attunement, local energy and energy meta-data. Our work contributes both a broader, more integrative design perspective on energy and materiality as we...