One of the key process steps in the compounding of polymers by extrusion is filtration, namely the elimination of all types of foreign particles. The market offers a range of different technologies for this. To permit the correct choice of filtration system, it is important to know the state of the starting material and have an overall view of the process chain. This article establishes the most important assessment criteria to serve as decision aids, such as continuity and discontinuity, constant pressure, contamination elimination capacity and the service life of the screens.