Buckminster Fuller's Montreal Biosphere (the US pavilion at Expo 67) is a radical solution to the problem of roofing a great volume with the least possible material: the geodesic dome. For Fuller the question is simple — how can a sphere (the form with the most efficient volume-to-surface ratio) be built lightly out of struts, without columns?

The answer is to divide the surface of the sphere into triangles. A polyhedral lattice approximating a sphere is woven from thousands of small triangles of steel tube. The triangle is the only geometric figure that does not deform within itself; so the lattice carries itself, distributing load evenly across the whole surface, with no need of any internal column or arch. The larger the structure grows, the more efficient it becomes: the bigger the dome, the smaller its own weight relative to the volume it encloses. This is a logic learned from the cell and crystal structures of nature — Fuller called it 'doing more with less' (ephemeralization).

The Montreal dome is a three-layer space frame about 76 metres in diameter, nearly a complete sphere, with suspended platforms inside. Clad outside in acrylic panels (which burned in a 1976 fire, leaving the steel skeleton), the dome is a manifesto of a structural type that is light, transportable, and theoretically able to grow without limit. The geodesic dome, carrying the shell-lattice logic to extreme efficiency, has deeply influenced both engineering and the idea of sustainable, low-material design.