This paper is focused on the preparation of novel hybrid polymer composite materials for 3D filaments. As the reinforcing filler, expanded graphite, carbon fibers, and combinations thereof were used in various ratios up to 10%. The mechanical and thermal properties of virgin and recycled polyethylene phthalate glycol-modified (PETG) composite materials were determined. Almost all prepared composite materials were suitable for 3D printing and they have enhanced mechanical properties compared to the neat PETG matrices. Addition of the fillers to both polymer matrices has an only slight effect on the thermal stability, but the addition of carbon fibers significantly reduced the thermal expansion coefficient. The composites from cheaper recycled PETG have comparable properties to virgin PETG composites, which is of economic and ecological importance. New and cheaper materials can help expand 3D printing to manufacturing plants and the use of 3D printers for special applications.