<p>Conventional multi-cell honeycombs excel in energy absorption but often incur high manufacturing costs. While assembling low-cost self-locking honeycombs offers a promising alternative, their crashworthiness is inherently compromised by local instability, particularly in configurations with fewer bent plates. To reconcile this trade-off between low-cost manufacturing and high energy-absorption efficiency, this study proposes a novel foam-filled self-locking honeycomb (FSLH). A comprehensive investigation combining out-of-plane compression tests and validated non-linear explicit dynamics simulations was conducted to systematically evaluate the effects of gradient foam densities, cell size, the number of bent plates, and dynamic impact velocities. The primary scientific contribution of this study lies in uncovering a scale-dependent and counter-intuitive topological coupling mechanism between the foam core and the self-locking walls. Specifically, while the specific energy absorption (SEA) of the empty structure dictates a positive correlation with the number of bent plates, the FSLH exhibits a reversed synergistic trend: reducing the number of bent plates optimally amplifies the lateral foam-wall interaction, thereby maximizing the overall SEA and fundamentally enhancing the deformation stability. Furthermore, the study evaluates the dynamic inertia responses, revealing that high-velocity impacts effectively suppress the initial peak force while generating denser progressive wrinkles. These novel findings provide a promising alternative for the design of energy-absorbing structures that are both cost-effective and highly efficient, offering new insights into the potential applications of foam-filled self-locking honeycomb structures in energy-absorption systems.</p>