Foster and Partners designed custom exterior, free-spanning louvers for this office building in Walbrook. The louvers are hollow and were manufactured by inflating the interior of a fiberglass and resin layup against a hollow mold. The louvers are lightweight, stiff, and weather well. The louvers’ shape is a complex curve, curving in both cross section and in plan. According to Detail, serial production was the most cost efficient way to make the louvers. The mold was designed to create repetitive cross section and plan curvatures, while allowing for varied lengths (Gabler 2008).