In a circular economy (CE), the economic and environmental value of materials is preserved for as long as possible by keeping them in the economic system, either by lengthening the life of the products formed from them or by looping them back in the system to be reused. The notion of waste no longer exists in a CE, because products and materials are, in principle, reused and cycled indefinitely. Taking this description as a starting point, the article asks which guiding principles, design strategies, and methods are required for circular product design and to what extent these differ from the principles, strategies, and methods of eco-design. The article argues that there is a fundamental distinction to be made between eco-design and circular product design and proceeds to develop, based on an extensive literature review, a set of new concepts and definitions, starting from a redefinition of product lifetime and introducing new terms such as presource and recovery horizon. The article then takes Walter Stahel's Inertia Principle as the guiding principle in circular product design and develops a typology of approaches for Design for Product Integrity, with a focus on tangible durable consumer products. The newly developed typology contributes to a deeper understanding of the CE as a concept and informs the discussion on the role of product design in a CE. Keywords:circular economy closed loop eco-design product design product durability remanufacturing Conflict of interest statement: The authors have no conflict to declare.

For product designers, the world has traditionally been one of resource abundance. Introducing them to a resource-constrained world thus requires new design strategies. This chapter explores how embedding circular economy principles into design practice and education could help product designers take critical material problems into account. We introduce four product design strategies that address materials criticality: (1) avoiding and (2) minimizing the use of critical materials, (3) designing products for prolonged use and reuse, and (4) designing products for recycling. The 'circular' strategies (3) and (4) are elaborated, as these sit most firmly within the remit of product design. This leads to a typology of circular product design that redefines product and material lifetime in terms of obsolescence, and introduces a range of approaches to resist, postpone or reverse product and material obsolescence. The typology establishes the basis for the field of circular product design, bringing together design approaches that were until this date unconnected and paving the way for the development of detailed design methods.

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