Plurality of tools and methods for circular design. Classification and stakeholder involvement for sustainable industrial innovation.

Integrating Circular Design (CD) into the early stages of New Product Development (NPD) is essential to reducing environmental impact, enabling a circular economic model, and complying with emerging European regulations. However, due to cultural, organisational, technical, and financial barriers, companies face significant challenges in adopting practical tools and methods to support this transition. This paper presents a critical and structured reworking of a previous classification of 77 circular design tools to support their application in industrial contexts. The analysis explores their characteristics, objectives, areas of intervention across the NPD process, and the levels of stakeholder involvement, interpreting the results through the lens of plural design principles. From this perspective, the study acknowledges the complexity of organisational contexts and the multiplicity of actors involved, while highlighting recurring challenges: the limited attention given to the active role of end-users, crucial in strategies such as product reuse, repair, and maintenance, the lack of sector-specific tools, and the insufficient support for cross-functional collaboration. As an extension of the original study, the tools were further analysed and grouped into homogeneous clusters, forming an operational framework grounded in the literature. This framework aims to guide designers and professionals in identifying the most appropriate tools for each phase of the NPD process, while also suggesting the company departments be involved and identifying potential synergies across functions. The research seeks to provide tangible support to designers, companies, and researchers by offering an integrated overview of existing tools and outlining new directions to make circular design more accessible, participatory, and interdisciplinary. This work systematically addresses contemporary environmental and social challenges by fostering collaboration between designers, users, communities, and enterprises.