Materials are the building blocks of society, making up the buildings, infrastructure, equipment and goods that enable businesses and people to carry out their daily activities. Economic development has historically coincided with increasing demand for materials, resulting in growing energy consumption and carbon dioxide (CO2) emissions from materials production. Clean energy transitions must decouple these trends. Material efficiency strategies can contribute to CO2 emissions reduction throughout value chains. Despite being an often overlooked emissions mitigation lever, opportunities for material efficiency exist at each lifecycle stage, from design and fabrication, through use and finally to end of life. Pushing these strategies to their practical yet achievable limits could enable considerable reductions in the demand for several key materials. Conversely, the demand for some materials may moderately increase while delivering favourable emissions benefits at other points in the value chain. As a result, improved material efficiency can reduce some of the deployment needs for other CO2 emissions mitigation options while achieving the same emissions reduction, thus contributing to clean energy transitions. This analysis examines the potential for material efficiency and the resulting energy and emissions impact for key energy-intensive materials: steel, cement and aluminium. It includes deep dives on the buildings construction and vehicles value chains, and outlines key policy and stakeholder actions to improve material efficiency. Important actions include: increasing material use data collection and benchmarking; improving consideration of the life-cycle impact in climate regulations and at the design stage; and promoting repurposing, reuse and recycling at end of product and buildings lifetimes.