This work intends to establish, by means of analytical modelling, a practical definition of the
superplastic behaviour by using the results of the free bulging of sheet metal instead of the results of the
traditional tensile test. In particular this paper analyses the superplastic flow of PbSn60 alloy and it
focuses the attention on the value of H parameter corresponding to the maximum value of dt/dH, never
considered in the literature. This parameter can represent a practical tool in industrial applications to
establish the superplastic behaviour of a sheet metal