This paper describes system cost based material selection, a computerized procedure for considering mechanical requirements, manufacturing costs, and material selection in the design of injection molded engineering thermoplastic parts. The benefit of this approach is the simultaneous consideration of material choice and part geometry on estimated manufacturing cost during candidate design selection. Using cost as a material selection measure permits the examination of system cost as a function of application requirements. The current implementation uses the allowable deflection of a flat plate and equivalent system stiffness as performance measures. Manufacturability concerns include required part thickness and gating scheme to adequately mold the part, production costs for meeting part tolerance requirements, and a resulting cycle time based on part cooling time estimates. Part manufacturing cost includes material cost, cycle time, and production costs. An example of a desktop printer shows the merits of this approach.