An improved two-phase model has been developed for a wiped film (third stage) polyester reactor. The model accounts for all the important main and side reactions and incorporates the effect of vaporization of four low molecular weight volatile species. Industrial data under three different operating conditions are used to obtain best-fit (tuned) values of the model parameters. When these values are used unchanged in the model, the latter predicts industrial operation under a fourth set of operating condition. This indicates that the 'tuned' model accounts for all the physico-chemical phenomena present in the reactor. A sensitivity study reveals the importance of some parameters and suggests that these should be determined experimentally using more basic experimental studies rather than by tuning industrial data wherein several additional physical phenomena are present.