Heinz Isler’s form-finding models for his “HIB” shells: between experiment and design Giulia Boller 1 [0000-0002-9903-4723], Philippe Block 2 and Joseph Schwartz 2 1 Department of Architecture, ETH Zurich boller@arch.ethz.ch 2 Department of Architecture, ETH Zurich Abstract. The Swiss engineer Heinz Isler (1926-2009) is among the most prominent figures in shell design. Thanks to a form-finding approach based on the use of physical models, he designed and built many shell projects in reinforced concrete. His unconventional structures still represent an important source of inspiration for today’s structural engineers. The paper reconstructs Isler’s experimental method by looking at the multiple physical form-finding models he developed for his tennis hall shells. Designed for the first time in 1977, they became one of Isler’s most successful shell typologies, promoted as “HIB” shells in Switzerland. Despite their apparently simple shape, Isler produced the largest number of physical form-finding models for this specific shell type. Their double symmetry challenged his design method: the highest precision was needed to avoid any irregularities in finding the appropriate geometry. By studying the original materials stored at the Heinz Isler Archive (gta Archives, ETH Zurich), details about Isler’s experimental approach to the conceptual design of his shell structures will be revealed for the first time. Keywords: Form finding, Reinforced concrete shells, Heinz Isler, Physical models, Conceptual Design. 1 Introduction Shells are among the most elegant structures. They combine their form with the most appropriate flow of forces. Thanks to their double curvature, they accommodate any load configuration through pure membrane action. In this context, form-finding methods help finding their appropriate equilibrium shape under boundary conditions, in compliance with external and internal forces. The foundations of computational form-finding tools were laid in early experiences with physical models [1]. Together with the German architect Frei Otto (1925-2015), and the Italian engineer Sergio Musmeci (1926-1981), the Swiss engineer Heinz Isler (1926-2009) is considered one of the masters of physical form-finding techniques in the second half of the 20th century [2]. This paper investigates Isler’s experimental form-finding approaches by looking at the models that were fabricated for the tennis hall projects. Such shells exemplified Isler’s ability in mastering his form-finding technique with physical models.