In Powder Injection Molding (PIM) and Fused Filament Fabrication (FFF) of ceramic and metallic components, thermoplastic polymer compounds are highly-filled with powder of the final material. These feedstocks are used to produce green parts. Later on, the polymeric components are removed in the debinding step and the final components are obtained by sintering. The rheological behavior of these feedstocks is critical for the shaping process and the final properties of the components. The flow behavior of the feedstocks is very sensitive to the amount of fillers in the liquid polymer, the particle size distribution and shape, the nature of the filler and the polymer matrix, and the use of coupling agents or compatibilisers. Several investigations on the influence of the particle size distribution and shape can be found. Here the nature of the filler is also investigated. Thus, three different types of particles were used: steel, aluminium and titanium. Comparable particle size distribution and shape were selected for the different fillers. The different fillers were compounded with a polymer/wax binder system with three different powder loadings. The plate-plate rheological measurements were done and significant differences were observed between the different compounds.