A
thermoplastic filament comprising multiple polymers of differing flow temperatures in a geometric arrangement and an interior channel containing a structural or functional thread therein is described. A method for producing such a filament is also described. Because of the difference in flow temperatures, there exists a temperature range at which one
polymer is mechanically stable while the other is flowable. This property is extremely useful for creating
thermoplastic monofilament feedstock for three-dimensionally printed parts, wherein the mechanically stable
polymer enables
geometric stability while the flowable
polymer can fill gaps and provide strong bonding and homogenization between deposited material lines and
layers. These multimaterial filaments can be produced via thermal drawing from a
thermoplastic preform, which itself can be three-dimensionally printed. Furthermore, the preform can be printed with precisely controlled and complex geometries, enabling the creation of a filament or
fiber with an interior thread contained within the outer, printed filament or
fiber. This thread adds structural reinforcement or functional properties, such as electrical
conductivity or optical waveguiding, to the filament.