## 1 Introduction  
In the next decade, the global composites market is expected to grow steadily, with an annual growth rate of 7.0% [1]. Regulations and legislation are progressively forcing a reduction in the polymer composite landfill, because they are imposing considerable costs for waste disposal landfilling in many countries, thus favoring the investigation of more valuable routes, such as recycling and reuse of End-of-Life (EoL) composites [2; 3; 4]. Therefore, there is an increasing demand for more application fields for composite materials at their EoL, especially in industrial sectors, such as automotive and transportation, since most research studies on the recycling and remanufacturing of fiber-reinforced polymers are originated in an academic context [5; 6]. This need can be fulfilled by developing and combining various strategies and approaches, such as those implemented in the frameworks of circular economy (CE) and cascading [7] and of Design for Sustainability [8], which have certainly fostered some examples of green design and eco-design principles. Moreover, the effectiveness of all these strategies for more sustainable development should be assessed quantitatively by using circularity metrics [9], which should monitor and minimize the environmental impact induced by circular and sustainable policies [10].  
To promote sustainable and environmentally-friendly development, manufacturing industries also need to improve product design and production processes [11], and this can be achieved by shifting to additive manufacturing (AM) technologies, which are able to support a more sustainable production than conventional manufacturing methods due to several AM sustainability advantages [12; 13; 14]. In the light of these benefits, AMtechnologies can also encourage the use of recycled glass fibers (rGFs) and carbon fibers (rCFs) without worsening performance when compared to virgin fibers [15; 16]. AM is already exploited in the automotive sector to produce spare parts, for which carbon fiber-filled thermoplastic composites were 3D printed to produce some components of out-of-production cars [17; 18]. However, there is a lack of AM adoption to produce real automotive components, especially exploiting rGFs and rCFs, as well as cross-linkable polymer matrices.  
This work explores the use of AM technologies to reprocess rGFs and rCFs for new applications in the automotive sector, aiming to foster real exploitations of rGFRPs and rCFRPs through 3D printing. In detail, it shows two possible workflows, indirect FFF 3D printing and UV-DIW. The experimentation comes from an industrial case study on reusable vehicle components and uses one part of a new concept of car structure as a benchmark. The two paths for the fabrication of the pieces are explained and discussed after describing the two process workflows and the industrial case study, supported by tensile tests. The preliminary results of this work validate the use of rGFRPs, rCFRPs and AM technologies for real applications in the automotive sector. As a result, the two approaches may be implemented in industrial contexts for small batches of customizable components and prototypes, paving the way for the practical implementation of these new recycled composite materials and AM technologies.