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In this study, the mechanical properties of polylactic acid (PLA), lightweight PLA (LW-PLA) filaments, and 3D printed cubes, were analyzed at various temperatures and infill densities. In terms of tensile properties, LW-PLA exhibited better ductility and toughness compared with PLA. Regarding thermal properties, LW-PLA showed a lower glass transition temperature and higher crystallization and melting temperatures with a double melting peak compared to PLA. Notably, LW-PLA foamed actively at temperatures above 220℃, and the most uniform foam structure was observed at 240℃. The foam structure of the LW-PLA changed depending on the temperature and infill density, confirming that the size, density, and surface quality of 3D printing samples can be controlled through these parameters. Because of foaming, the size of 3D printed cubes increased, whereas their densities decreased. As the temperature increased, the initial elastic modulus of the LW-PLA decreased, and it was confirmed that the foam structure formed by bubbles absorbed the pressure. Specifically, the compressive stress of LW-PLA-240-100 decreased despite the high infill density, whereas its toughness was maintained or increased. This indicates that the foaming characteristics provide excellent energy absorption. Based on this study, it is possible to achieve suitable foaming characteristics for specific applications by controlling the temperature and infill density.