The great influence of temperature on polymer's behavior is well known and, for example, a 10°C increase can lead to a 10 time reduction of the viscosity. The necessity to take into account the self heating phenomena appears then to be crucial for thermoforming process simulation and in particular for ISBM of PET. An original anisotropic visco-hyperelastic model coupled with temperature has been developed [1,2], identified from equibiaxial and constant width tension tests [3] and can be used to evaluate this self-heating phenomenon. In order to provide validation of the model and its capacity to predict accurately final bubble shape, self-heating value and induced mechanical properties, free blowing of a preform has been carried out with temperature measured using a thermal camera. Results are discussed and compared with numerical simulation prediction. At room temperature, tension specimens have been cut from the different blown bubbles and induced modulus where measured in three directions: longitudinal and hoop directions and also 45° from both previous ones and an elastic orthotropic behavior is identified. The effect of the self heating on the free blown shapes and induced modulus is discussed.