Abstract: Disclosed is a composite filament with high densities designed for additive manufacturing. The composite filament can be used with for fused filament fabrication. Additionally disclosed are methods for its production and application. The composite filament comprises a continuous elongate structure made from a polymer binder (e.g., a high glass transition temperature polymer) combined with various metals at adjustable concentrations. The filament is created by extruding a mixture of polymer and metal, allowing customization of the filament's density through compositional adjustments. Additionally, the disclosure encompasses three-dimensional objects produced with the filament and the processes for their fabrication.