Natural materials are attracting the interest of researchers as reinforcements in polymer composites because of their low cost, light weight, good mechanical properties, and biodegradability. Numerous studies are being conducted focusing on the search for composites that integrate the use of various natural materials as reinforcement with their potential applications in different areas of industry. Polymer composite materials are typically produced using classical methods; however, with the development of manufacturing techniques, they have also become a subject of research in the field of additive manufacturing. This study examined the effect of natural fillers in the form of fibers and powders on thermal degradation, density, water absorption, shrinkage, tensile strength, and impact strength. The samples were made using additive manufacturing with the extrusion technology - MEX (Material Extrusion) at fixed process parameters for each material. The analysis included commercially available materials with a polylactic acid (PLA) matrix at 40 vol.% addition of wood, bamboo, and cork, and the results were compared with those of the pure material. The studies showed that the applied natural fillers reduced the density (max. 6%) and tensile strength (approximately 30%), but improved the impact strength (up to 45%). In turn, water absorption increased significantly due to the presence of natural fillers (up to 5.8 times more on the first day). Furthermore, materials containing natural fillers decompose faster, reducing the thermal stability of the composites.