In this study, the mechanical behavior of bio-inspired lattice structures under quasi-static compressive loading was experimentally investigated. The geometries examined included a conventional honeycomb structure, a sunflower-inspired structure, and a hybrid structure obtained by combining the spiral arrangement of sunflower patterns with re-entrant geometry. Despite many studies on auxetic, nature-inspired, and foam-filled structures, the combined effects of sunflower-inspired radial arrangement, re-entrant geometry, and foam filling on energy absorption remain unexplored. Addressing this gap, this work designs and experimentally evaluates a foam-filled bio-inspired auxetic structure using radial gradation, negative Poisson’s ratio geometry, and polyurethane foam to enhance absorption.The specimens were fabricated using three-dimensional (3D) printing technology with polylactic acid (PLA) material and were tested in both hollow and foam-filled configurations. The results demonstrated that the cellular geometry plays a significant role in the buckling mechanism, deformation stability, and energy absorption capacity. The hybrid sunflower–re-entrant structure exhibited a more uniform stress distribution and a more progressive collapse mode than the conventional honeycomb structure due to its auxetic behavior and radial–spiral arrangement. Furthermore, the addition of polyurethane foam increased the initial stiffness, delayed the onset of buckling, and improved the progressive crushing behavior. Experimental results revealed that the proposed structure achieved a 112% increase in energy absorption, a 6% improvement in specific energy absorption, and a 3% enhancement in crushing force efficiency compared with the conventional honeycomb structure. These findings suggest that the proposed structure has considerable potential for use as an energy absorber in aerospace, automotive, and sandwich panel applications.