As to the isothermicity of the translucent walls, experimental laboratories will be able in the near future to give us a new translucent material whose isothermal properties will be equal to that of the thickest wall. From then on, we will witness the inauguration of a new era: buildings will be altogether hermetically closed. Windows will no longer be needed on the façade; consequently neither dust nor flies nor mosquitoes will enter the houses; nor will noise.

Le Corbusier's fascination with light and glass formed a continuing thread throughout his career. After his maxim ‘architecture is lighted floors’ came the passionate discourses to defend the building's openness, first with his fenêtre en longueur, the ribbon window, and ultimately with his emblematic pan de verre, the glass wall that would not only provide sunlight-flooded interiors but would also most significantly contribute to shape the Modernist imagery. Despite the profuse explorations invested in this concept, Le Corbusier would always lament his failure to execute his ‘pan de verre 100%’ in the way he would have desired: ‘as a mur neutralisant constituted by a double glass-wall with an internal cavity through which conditioned air would circulate, hot in winter, cold in summer’.

The idea of the mur neutralisant was born as part of a challenging environmental theory for buildings, termed either respiration exacte or air exact [1], proposed by Le Corbusier in collaboration with his cousin and practice partner Pierre Jeanneret in 1928. Le Corbusier would describe this theory in two of his most dogmatic publications: first, as one of his lectures (5 October 1929) collected in Précisions (1930) and, second, as part of La Ville Radieuse (1935), his manifesto on modern habitation.