In our built environment, flat glass is an indispensable material. Its production requires the mining of raw materials and the use of fossil fuels and results in the emission of pollutants including CO2. In Western European countries, these emissions have been the target of a series of energy efficiency measures and emission reduction policies since 1945. Beginning with that year, this article studies the material history of the flat glass industry in Belgium, France and the EU and analyses the evolution of the flows of materials, energy and CO2 related to the manufacturing process. Based on a retrospective material and energy flow analysis (MEFA), the objective is to assess the environmental footprint of the architectural flat glass sector and to provide an understanding of the socioecological patterns that have shaped its metabolism. Based on an extensive data collection, this paper is the first publication of long-term time series on the manufacturing of architectural glass. The findings reveal two major concerns: on the one hand, energy efficiency measures have weakened ever since the 1990s, despite the tightening of the European environmental policies; on the other hand, the demand for architectural glass in the EU remains particularly high, resulting in a production rate that uses considerable energy and exploits a large amount of raw materials. The relative decoupling of the energy and CO2 intensities seems to have reached a threshold and has not resulted in an absolute decoupling of environmental burdens from industrial growth. We discuss measures and research needs to support a decarbonisation of the flat glass sector. ; SCOPUS: ar.j ; info:eu-repo/semantics/published