jats:p This paper presents an iterative method for the design of structurally optimised, simply supported, flexibly formed, concrete beams. The design and construction method using flexible formwork has been shown to facilitate material savings of up to 40%, providing significant opportunities for low-carbon-dioxide concrete design. The proposed method considers both ultimate and serviceability limit states for the optimised beam. The iterative nature of the design process, and its interdependency with the construction method, is demonstrated. Further considerations such as reinforcement detailing, methods to support the flexible mould and alternative support conditions are also discussed. It is demonstrated that replacing conventional orthogonal moulds with a flexible system composed primarily of high-strength, low-cost fabric sheets, utilises concrete to create extraordinary possibilities for highly optimised, low-carbon-dioxide, architecturally interesting building forms. </jats:p>