This paper presents a detailed case study on the effective upcycling of a post-industrial plastic waste stream to a renewed compound, fit for re-use in a new application. The material investigated was a PET-contaminated recycled PP, destined for a high-impact, medium-stiffness application. After two research trials and one large-scale industrial trial, an upcycling formulation was determined to bring the recyclate to the required level of the new application, thus closing this specific material loop within the case company. The used methodology adheres to the Design from Recycling principle, in which industrially available (mechanically) recycled polymer materials are matched to potential new products. The design strategy starts from either the properties of an available recycled polymer (and then defines the product) or from the functional boundary conditions of the product (and then selects the material and/or an optional material upcycling step). The Design from Recycling principles can elegantly be combined with those of Design for Recycling, within the framework of a Circular Economy. POLYM. ENG. SCI., 58:528-534, 2018. (c) 2017 Society of Plastics Engineers