The paper presents a method, developed by the authors, for manufacturing polymer composites with the matrix manufactured in a layered manner (via 3D printing – Fused Deposition Modeling) out of a thermoplastic material. As an example of practical application of this method, functional prototypes are presented, which were used as elements of foundry tooling – patterns for sand molding. In case of manufacturing prototype castings or short series of products, foundries usually cooperate with modeling studios, which produce patterns by conventional, subtractive manufacturing technologies. If patterns have complex shapes, this results in high manufacturing costs and significantly longer time of tooling preparation. The method proposed by the authors allows manufacturing functional prototypes in a short time thanks to utilizing capabilities of additive manufacturing (3D printing) technology. Thanks to using two types of materials simultaneously (ABS combined with chemically hardened resins), the produced prototypes are capable of carrying increased loads. Moreover, the method developed by the authors is characterized by manufacturing costs lower than in the basic technology of Fused Deposition Modeling. During the presented studies, the pattern was produced as a polymer composite and it was used to prepare a mold and a set of metal castings.