Additive manufacturing enables the fabrication of lightweight cellular lattices with tailorable mechanical behavior. This study examines the low-velocity impact response of thermoplastic polyurethane (TPU) honeycombs produced by fused filament fabrication (FFF) and tested using an Open Hopkinson Pressure Bar (OHPB) system. Five topologies¿square (Sqr), hexagonal (Hex-0° and Hex-90°), and re-entrant (Re-ent-0° and Re-ent-90°)¿were designed with the same volume fraction and evaluated through force¿displacement analysis at a nominal impact velocity of 9 m/s. The square topology exhibited the highest peak force, about 80% greater than the auxetic Re-ent-0° configuration, while the rotated hexagonal lattice (Hex-90°) demonstrated the highest energy absorption, reaching values approximately 60% higher than Re-ent-0°¿while maintaining moderate stiffness. Re-entrant lattices provided more compliant responses dominated by folding and buckling, whereas square and hexagonal lattices resisted higher loads over shorter displacement ranges. All structures showed substantial shape recovery after impact, indicating the predominantly elastic and reversible response of the TPU walls under impact loading. These experimental results highlight the influence of lattice topology on the stiffness¿energy dissipation balance in flexible honeycombs, demonstrating their potential for reusable energy-absorbing applications such as footwear, protective equipment, and soft robotics.
