Wallness, through technical and cultural considerations, overturns the act of building and opens up a conversation. Insulation is now an integral part of the repertoire of architectural elements, while thermal engineering reveals unsuspected fields of construction. The quest for comfort in interior spaces calls into question the nature of the building envelope. Wallness expands the role of the wall, summoning up all its components and defining a new rationality. The issue of transparency is no longer limited to the visible, but extends to all the invisible chemical and physical phenomena passing through the wall. Wallness sees the solid as both a necessity and an unprecedented formal potential. As always, materials are at the heart of the revolution.