The article presents analysis of mechanical properties of specimens fabricated by fused deposition modeling (FDM). The four of considered materials are the well-known 3D printing filaments i.e., polylactide (PLA), Nylon 12 (PA12), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol (PET-G). The other four of the considered materials are composites with carbon i.e. polylactide with carbon fiber (PLA-CF), Nylon 12 with carbon fiber (PA12-CF), acrylonitrile butadiene styrene with carbon fiber (ABS-CF), polyethylene terephthalate glycol with carbon fiber (PETG-CF). The paper describes how the specimens were designed, printed, subjected to tensile testing, and examined using microscopy. The obtained data will be used to select the optimum material for the rapid manufacture of lower limb orthoses. Carbon composites were found to have better mechanical properties of their base material, but the fabrication of composite samples is much more time consuming, for the reason that the manufacturing process is not stable.