The last decades have witnessed a significant development and increased usage of additive manufacturing (AM) technologies. Among these technologies, the fused filament fabrication (FFF) is being characterized by a massive worldwide spreading, from specialized companies with high-quality equipment to the hobbyist with home-made 3D printers. Thus, and aiming to help the user achieving the best results, it is essential to continuously perform studies and analyses concerning the mechanical properties resulting from different feedstock materials and printing settings. This study covers the execution and the subsequent comparative analysis of the results of flexural and tensile tests on three different types of FFF materials: polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and CarbonFilTM. It also comprehends a parallel study of the infill setting, more specifically the testing of specimens with a 50% infill reduction. All tests were executed according to the corresponding American Society for Testing and Materials (ASTM) standards. This work aims to clarify the properties of three different materials and the effect of the internal material reduction on the mechanical properties of 3D printed objects.