architects who embrace the expression of Western and Eastern building forms and methods. Perhaps most influential from Hejduk was the study of the structure of architectural systems. Ban is most famous now for his innovative work with paper and cardboard tubing as a building material. He was the first architect in Japan to construct a building primarily out of paper with his paper house, and required special approval for his building to pass Japan's building code. Ban is attracted to using paper because it is low cost, recyclable, low-tech and replaceable. The last aspect of Ban's influences is his humanitarianism and his attraction to ecological architecture. Ban's work with paper and other materials is heavily based on its sustainability and because it produces very little waste. As a result of this, Ban's DIY refugee shelters (used in Japan after the Kobe earthquake, in Turkey, Rwanda and around the world) are very popular and effective for low-cost disaster relief-housing. Ban created the Japanese pavilion building at Expo 2000 in Hanover, Germany in collaboration with the architect Frei Otto and structural engineers Buro Happold. The 72-metre-long gridshell structure was made with paper tubes. But due to stringent building laws in Germany, the roof had to be reinforced with a substructure. After the exhibition the structure was recycled and returned to paper pulp. Ban fits well into the category of "Ecological Architects" but he also can make solid claims for being modernist, a Japanese experimentalist, as well as a rationalist. Natias Neutert, German thinker, critic, and poet, marks Ban in his essay as "a gentle revolutionary ... guiding contemporary architecture towards transparency, the spherical and the open". Ban himself quotes: "I don't like waste", summing up his philosophy and practice, known as "Paper Architecture". In June 2020, he and other architects, as well as chefs, Nobel laureates in Economics and leaders of international organizations, signed the appeal in favour of the purple economy (“Towards a cultural renaissance of the economy”), published in Corriere della Sera, El País and Le Monde. Use of paper as a building material Ban's experimental development of paper tubing structures came in 1986, before any of his programmatic commissions. He found paper's structural integrity to be much better than expected and noted that it is also available all around the world. The structures are most commonly available from manufacturers providing paper tubes for use in textile factories, as in