Frei Otto began working on lightweight structures amid post-war material shortage and, at the institute he founded in Stuttgart, made finding form rather than calculating it a method: soap films, hanging chain nets and elastic models produced surfaces that became optimal by themselves under tension. A soap film finds, for a given boundary, the surface of least area; the architect's job was to measure that form and make it buildable.

The roof designed with Günter Behnisch for the 1972 Munich Olympics is the largest application of the method: a single steel net with acrylic panels covers the stadium, the sports hall and the swimming pool. The design carried a political programme as well — against the heavy monumental architecture of the 1936 Berlin Olympics it set an image of a transparent, light and non-authoritarian Germany.

Calculating the structure pushed the computers of the day; solving the forces at the net's thousands of nodes is an early instance of numerical form-finding in architecture, and the ancestor of today's parametric design. Membrane and net systems working in tension spread from airport terminals to stadiums. Otto's real legacy is not a style but a criterion: a structure is judged by how little material it uses to carry its load. He was awarded the Pritzker Prize in 2015 and died days before the announcement.