Béton brut and ineffable space: two concepts defined by Le Corbusier after World War II that speak about a stronger dialogue between materials and artistic vision of his work. Invented to designate his own particular use of exposed concrete, béton brut is analysed from different perspectives: its fabrication with a rigorous selection of its constituent materials; its textural imprint obtained by a refined assembly of formwork; and the treatment of its surface with special types of paint. In the synthesis of his artistic vision, ineffable space is explained in all its forms and meanings, from the insertion of the tapestries and paint in the qualification of the spaces, to the way in which photography is used to study the unexpressed potentialities of architecture and painting. The genesis of Le Corbusier's work, the quality of constructions materials and questions of optics, artistic vision and the psychophysiology of perception are analysed in relationship with the contemporary artistic phenomena such as the automatisms of Breton, the Art Brut of Dubuffet, the Concrete Music of Varèse, Klein's research on monochromes, Pop Art and the concept of transfer. In this essay, a new vision is revealed about the last and fundamental works of Le Corbusier.