Polymer films are used in the packaging of industrial and food products. Effective thermal bonding of the films requires that the interface between layers must be at least partially melted. There are limitations of the temperature of the heat seal, as too high a temperature could cause sticking of the films to the surface of the heat seal unit, and too low a temperature would affect throughput, ie sealing strength. To understand the problems and to be able to consider changes in operating conditions it is necessary to have a reliable model that predicts the temperature distribution of the film during heat sealing, and calculates the necessary dwell time to fuse the layers of the polymer. In developing heat transfer and energy balance models of the process it is necessary to realize the complexity of the problem, i.e., transient heat conduction in a composite solid material with multidimensional geometry. The situation is further complicated by the latent heat of fusion effects, incomplete/non-uniform contact of heat seal with the polymer, and the possible variation of properties upon heating. It is evident in other engineering applications that the control and accuracy of such models facilitate scale-up and improvement of existing systems as well as analysis of new applications. The development of an exact solution to the problem is possible, under some hypothesis. The model verification with computer package to predict the temperature distribution is discussed.