A so called `three-section¿ model for air bending is presented. It is assumed that a state of plane strain exists and that Bernoulli's law is valid. The material behaviour is described with Swift's equation, and the change of Young's modulus under deformation is addressed. As compared with other models, the model described in the paper is capable of generating information such as required punch displacement and the unfolded blank size, very accurately. With in-process measurement of the spring-back angle, the punch displacement can be calculated even more accurately.