Extrusion dies exert influence on later final product quality. Therefore it´ll make a point the dimensional and die design by using programs for calculation and simulation frequently. For the implementation of product design, it is significant to understand the flow conditions and to be able to predict the flow behaviour accurately. Special rheological flow phenomena in the plastic melt as cross flows, which flow perpendicular to the main flow, should be taken into account. This phenomenon is caused by pressure gradients transverse to the direction of extrusion and both the flow distribution and the pressure consumption are influenced in the die. Network theory is a simple numerical method for a holistic one-dimensional representation (GEB) in a spreadsheet program (p.e. Excel), which can design an optimal uniform flow rate distribution and low pressure drop. The cross flow behaviour can´t be described with this method as yet. Therefor a linear equation system according to the Gauss algorhythm was developed, which can calculate the cross flows in the die with rectangle cross-section. In this network crosslinks are implemented to take into account the cross flows. The equation system is set up from the network, which corresponds to the number of the desired partial volume flows in the number of established equations. Furthermore the technical measurement entry of cross flows was conduced about the evaluation of ellipsoid shape according to the flow direction and the alignment according to the flow direction. Dead-stop experiments were performed by adding a blowing agent to the extrusion process. Negatives of die with gas-filled bubbles were prepared and evaluated with image analysis software across the half width of die. Afterwards the network theory was validated by Computional Fluid Dynamics (CFD).