Material efficiency (ME) refers to meeting human needs through minimal material production and processing. Key examples of strategies at various stages include the following: Design Stage • Light weighting: This strategy manufactures products using fewer materials while maintaining the same functionality. E.g. for vehicles, light weighting occurs through shaping components made of conventional steel to be thinner; and substituting conventional steel with lighter materials such as aluminium and carbon fibre-reinforced plastics. • Optimized Design: Design optimization could be facilitated through different production frameworks. E.g. using additive manufacturing, GE Aviation reduced the weight of its jet engines by approximately 25%, reducing the complexity from 18 parts to a single part. • Long-Life Design: Designing products to maximize lifespan could result in higher initial material demand but enables outweighing life-cycle emissions savings. E.g. in the construction sector, non-residential buildings have relatively short lifespans of less than 50 years. However, they could last for 70-100 years or longer. If a building is designed in a way that it can easily be repurposed and re-adapted for another use instead of being demolished, producing materials for a new building would be avoided. Fabrication Stage • Reduction of Material Losses: Reducing waste and overuse when manufacturing materials during production and in construction. E.g. construction companies often order more cement than that prescribed to avoid running out due to spillage, overuse, etc. While over-ordered unmixed bagged cement can be used elsewhere, over-ordered ready-mix concrete cannot usually be channeled to other uses before it becomes unusable. Improving architectural/engineering specification of cement or finding opportunities to use over-ordered mixed/unmixed cement, can reduce losses. • Substitution of Input Material: Higher-emissions materials can be substituted by lower-emissions materials. E.g. cement producers can replace a portion of higher-emission clinker with lower-emission alternative cement constituents, such as ground granulated blast furnace slag, fly ash and calcined clay. In construction, a portion of cement or steel could be replaced by sustainably sourced timber or other bio-based materials. Use Stage • More intensive use & Lifetime extension: Using a product for a longer time could reduce the material need for new products. This may mean extending the lifetime for current users or repurposing the product for other users. E.g. non-residential buildings could be repurposed for other uses to extend the lives of the structures. Normalizing reusable products and repairing broken products would reduce the need for new materials. End of life Stage • Reuse: Reusing a product/material prevents the need for new production and can occur in various forms, including e.g. Relocating (components are used in another same type product for the same purpose with little refurbishment); Refurbishing (components are used in another same type product for the same purpose after significant repair and reconditioning); Cascading (components are used in a different type of product with little reconditioning); Re-forming (components are used in a different type of product after significant repair and reconditioning) • Recycling: Although recycling consumes energy, the consumption is generally substantially less than producing primary materials. E.g. producing crude steel from scrap consumes three times less energy