Granulation is an important particle-size enlargement process, used in many industrial applications. Granulation within the pharmaceutical industry has, for many years, been performed through the adoption of a batch process. However, the technique of using a co-rotating twin screw granulator has been found to be very effective at granulating. The quality and manufacturing attributes of the granules produced vary depending upon a number of different machine and powder parameters. The focus of the work described within this paper has been on the crucial role that effective and accurate feeding of powders plays in the successful production of acceptable granules. This paper looks at both rigid frame and flexible frame LIW designs and also compares the performance across two scales of feeder from within the same commercially available product family. This work was performed using an active pharmaceutical ingredient (API) and this component was the major constituent of the formulation investigated. Consequently the physical properties of this API were the major contributing factors to the poor flow properties described within this paper. As a consequence of the physical properties of the pharmaceutical formulation under investigation, the rigid frame feeder, which used a fine pitch concave twin screw assembly to convey powders, was unable to accurately deliver the blended materials successfully. This was due to the blend bridging (or rat holing) within the powder hopper while under the influence of the bridge breaking scimitar blade. The material that was successfully delivered to the conveyance section of the feeder was then quickly over worked by the twin screws as a result of the feeder design. This resulted in the feeder motor shutting down as the upper control limit for motor power was exceeded. In contrast, the flexible frame LIW feeder only uses a single screw and has a spiral screw which is able to convey low bulk density powders more effectively. Additionally the flexible wall within the powder hopper is more effective at bridge breaking within the hopper should the powder consolidate. This resulted in efficient transfer of materials from bulk storage within the hopper to the single auger screw feeder which was connected upstream of the twin screw granulator. (C) 2012 Elsevier B.V. All rights reserved.