Material extrusion additive manufacturing with filaments is also known as Fused Filament Fabrication (FFF). FFF is a versatile and popular technology that, when combined with debinding and sintering, can be used for the fabrication of functional metal and/or ceramic parts similar to Powder Injection Moulding (PIM). In order to produce filaments, that are processable by FFF, a complex binder system is needed. The binder is generally composed of the main binder component, the backbone and additives. One popular additive in feedstocks for FFF or PIM is stearic acid (SA), since the use of SA is an effective way to reduce the viscosity, improve the feedstocks homogeneity and increase the solvent debinding rate.. In this investigation, the incorporation of SA into a binder system comprising of acrylic acid-grafted high density polyethylene, paraffin wax and styrene-ethylene/butylene-styrene copolymer has been studied. The effect of the SA on the viscosity, mechanical properties, debinding rate and processing by FFF for zirconia feedstocks is presented.