One of the most difficult problems in polymer processing analysis is to determine the state condition (viscoelastic, viscous) of these materials. In this paper, firstly a brief description of the basic processes that are involved in producing thermoplastic articles is stated. This is followed by a review of the various approaches that have been made to determine the equations: of state of polymer melts. Based on the analysis of these factors a flow chart for determining the state condition of plastics during the process is given. Finally, an application to coextrusion of film processing is submitted.