In this work the course of state in the pvT behavior during the injection molding of a plastic lens is investigated. The Tait equation describing the equilibrium pvT behavior of amorphous polymers is extended to non-equilibrium state by considering the cooling effect on the phase transition. Moreover, a special numerical method is developed to evaluate the cooling dynamics of the irregular-shaped lens. By means of methodology developed in this work, the cooling and pvT behavior as well as the thermal shrinkage of the injection-molded lens can be predicted.