A feedstock material for use as a support material in an additive manufacturing system includes a pre-ceramic material in powder form. The preceramic material comprises calcium carbonate, sodium carbonate, sodium aluminate or combinations thereof. The feedstock material includes a thermoplastic binder having the pre-ceramic material dispersed therein, wherein the pre-ceramic material and the thermoplastic binder are in a filament form. The filament is configured to be melted and extruded to form a support structure for a ceramifable article in a layer by layer manner, wherein the pre-ceramic material is at least about 50% of the feedstock material.