This article explores the rise of a new generation of practices combining architecture, design, and art, trying to answer the transition issues faced by society. It develops original operating procedures, including public participation. In doing so, those so-called “specialised” professions expand their sphere of operation and incorporate more immaterial dimensions and resources. The main objective of the article is an attempt to clarify how participation is embodied in specific intervention methods, within those experimental practices. The article will take as a case study a participatory project taking place in a retirement home and aimed at building a mobile third place that brought together various professionals coming from those experimental practices. The study of the participatory project will outline three devices and methods supporting the participation work, as follows: the use of permanence, the use of the prototype and self-construction, and the conception of ephemeral production. The article suggests that based on their analysis, we can understand what architects and designers “manufacture” through the agency of participation. Or more accurately, what participation “manufactures” in those experimental practices. The main result of the article is that the participatory project is more concerned with the motives and aspirations of the design activity, its methods and processes, its context and socialisation than it is with what would be classically considered as the outcome or result (the work, the realisation, the production, the built).