Abstract: To achieve the synergistic improvement of load-bearing stability and energy absorption in lightweight protective structures, a bio-inspired thin-walled-foam composite structure based on mechanical matching design is proposed. Three configurations of polylactic acid (PLA) bio-inspired shells were fabricated via additive manufacturing and subsequently filled with polyurethane foam through an in-situ foaming process. Tensile tests, quasi-static compression experiments, and drop-weight impact tests were conducted to investigate the effects of foaming-induced thermal conditions on the mechanical properties of the PLA shells and the structural response of the composites. Crashworthiness was evaluated using peak force, plateau force, specific energy absorption (SEA), mean crushing force (MCF), and crushing force efficiency (CFE). Results show that the temperature rise during foaming reduces the elastic modulus and strength of PLA while improving its ductility, thereby enhancing the mechanical compatibility between the shell and foam. Consequently, the composite structures exhibit significantly increased plateau force and MCF, and their collapse mode transforms from local instability to progressive stacked crushing, leading to stable hierarchical energy absorption. Dynamic impact tests further demonstrate the superior load-bearing and energy absorption performance of the composite structures under high-energy impact. The results highlight the synergistic role of geometric configuration, material matching, and thermal-mechanical coupling in regulating the energy absorption behavior, providing guidance for the design of lightweight bio-inspired protective structures.