Conveying of bulk materials in the hopper and feed zone of single screw extruders can be challenging for materials which show a wide variation of particle shape and size like regrinded materials. Therefore this study presents an adapted fluidization testing method which is known for powders, e. g. SLS-materials. The test comprises a rotating barrel with transparent covers which is partially filled with bulk material. Due to the rotation the material moves in the barrel and forms characteristic surfaces which can be quantitatively described by the avalanche height and angle. The study deals with the design of such a device for typical particle sizes for single screw extruders (characteristic particle dimensions of several millimeters). The impact of barrel geometry, barrel wall surface properties, rotation speed and bulk material properties is investigated in order to provide a test setup which yields reproducible and applicable results. The test setup is automated and features digital image processing in order to derive the avalanche height and angle for the characteristic surfaces and movements. Test results for virgin and regranulated bulk materials are presented. The applicability is shown by correlating avalanche height and angle with the throughput and flow steadiness of the bulk material through different hopper designs. These results offer support for single screw extruder design. It can also be used for incoming goods inspection and testing in order to assure processability.