The objective of this project is to develop a model for PET (Polyethylene Terephthalate) to determine the Young’s modulus at room temperature as a function of thermal and strain history. This is achieved through an inverse an inverse analysis whereby PET pre-forms are heated above glass transition temperature (~100°C) and bi-axially stretch blown without a mould whilst monitored via high speed camera. The strain fields during blowing are obtained through Digital Image Correlation (DIC). The free-blown containers are then subsequently pressurised at room temperature within the linear deformation ranges whilst monitored by a camera. From anisotropic Hooke’s law and the virtual fields method, the corresponding room temperature Young’s modulus in the axial and hoop direction is obtained on the free-blown bottle.