In a context of demographic growth and rapid urbanization of Khartoum and Cairo, the Sudanese and Egyptian red brick supply chains are regularly submitted to a strong technical criticism, especially regarding their environmental consequences (air and soil pollution, deforestation, encroachment on agricultural areas...) (Alam, 2006). Nevertheless, in order to be better understood, these speeches and policies are to be replaced in a more global approach, at the scale of the construction sector and of the planning policies in both capitals. In Northern contexts, building materials have been the subject of many metabolic studies, stressing especially on the energy and waste recycling issues (Mongeard, 2017; Augiseau, 2019; Bastin, 2019 ; Bastin, Verdeil, 2020). However, in order to deepen the political aspect of these metabolic systems and extend this methodology to other areas, this presentation proposes to associate it with other theoretical frameworks. The socio-technical analysis (Akrich, 1987) and the more general "material turn" in social sciences (Law, Mol, 1995; Whatmore, 2006; Ingold, 2012) can be articulated to metabolic studies. Resulting from these debates, some researchers have linked building materials sectors with political, urban and environmental aspects (Myers, 1999 ; Fry, 2014 ; Choplin, 2020 ; Achambault, 2021). Following on from these approaches, the presentation would show that building materials are at the intersection of different sets of policies, affecting each step of the supply chain (production, marketing, building). This proposal is based on several field surveys (February-March 2020 and April 2021 in Khartoum, February-March and May 2021 in Cairo), during which I conducted about 90 informal and semi-directive interviews with actors at all stages of the sector (producers, workers, site managers, architects, engineers, etc.). I will also rely on a complementary coming field survey in both capitals for my PhD's second year (February-June 2022). This empiric data is providing a comprehensive view of the supply chains and their functioning, but also details about the speeches of different actors organizing and regulating them. Both case studies are different in many ways (raw material used, localization, level of industrialization, etc.), but are subjected to common marginalization processes. Although the policies regarding construction sector, housing and urban planning might seem disconnected, I would try to show that they are integrated in a more general and comprehensive vision of the city. For example, the fight of the Egyptian state against informal areas in Cairo, in which the inhabitants are mainly using red bricks, can be associated to the decrees imposing the use of an expensive natural gas instead of cheap fuel oil in the red brick factories, but also to the increasing influence of the army on cement production. In Khartoum, the criticism of environmental pollution caused by the workshops on the banks of the Nile is to be linked with the predation of public and private actors for this coveted areas. In other terms, policy makers (mainly public actors, but often relying on private or academic analysis and support) are taking advantage of the metabolic and systemic functioning of the building materials sector in order to promote an urban model based on ideals of modernity and industrialized economy, as opposed to "informal" ways of producing and building. Therefore, the main goal of this oral communication would be to propose a critical eye on these technical and environmental speeches and policies about the building materials metabolism (production, circulation and use) in Khartoum and Cairo. Thus, it would try to deconstruct these representations and link it to the imaginaries and political strategies on which they actually rely.