This study investigates the impact response of auxetic and conventional hexagonal honeycomb lattices designed for sports protection via systematic experimental testing, interpreted by a predictive analytical model. The structures, fabricated from thermoplastic polyurethane (TPU) using HP Multi Jet Fusion 3D printing, were designed with matched mass and thickness for fair comparison. Impact tests were conducted following ISO 1621-1 standards for back protectors, and the transmitted forces were measured. Experimental results revealed while the hexagonal lattice transmitted lower forces under low-energy impacts, the auxetic structures, especially those with graded wall thickness, outperformed at higher energies, significantly reducing the transmitted force and thus offering enhanced protection. To interpret the experiments, an equivalent mass–spring model was developed. The model incorporates a nonlinear spring, based on quasistatic compression behavior, and a strain-dependent effective mass to capture densification effects observed in auxetic lattices during impact. These findings emphasize not only the superior performance of auxetic and non-uniform designs in high-impact conditions, but also the utility of simple yet effective models to guide rapid prototyping and optimization.
