"is a reinforced concrete shell with the shell thickness varying from 9 cm to 12 cm [3.5 to 4.7 in.]... Since the structure is in compression, instability is an issue, particularly at the edges and supports of the shell. Isler does not use any stiffening edge beams in the Naturtheater Grötzingen; instead, he upturns the edges (which corresponds to the overhanging fabric in the hanging model) so that the double curvature required for increased stiffness is achieved without any increase in shell thickness... However, to reduce the stresses in the supports, Isler simply tapered the legs so that they were thicker than the rest of the shell."