This work covers a new model to compute flat dies for the production of biaxially oriented polypropylene film. The computational model was developed in the late eighties and is particularly suited for dies of high throughout and width. In the development of new dies for our production lines, it was realised that all models known at the time we began this work had failed. These models only accounted for viscous flow in the die channels under ideal conditions. Temperature differences in the melt and the elastic behaviour of the die walls were not accounted for in those models. The new model allowed us to design dies for high throughput with no difficulties. With the model we were now able to provide our production with dies of optimal design. Before the model is explained in detail, the production process for biaxially oriented polypropylene film is sketched and the market demand for suck films is explained.