Objective Wood, as a natural porous material, holds significant potential in protective applications. However, its complex hierarchical pore structure and anisotropy limit the applicability of existing energy absorption theories developed for synthetic materials, thereby hindering precise design and high-value utilization in shock absorption. To address this, this study compares two representative wood species—softwood and hardwood—with equal-density, systematically investigating how their microstructural pore architectures influence compressive energy absorption behavior. The findings aim to provide theoretical foundations for scientific selection, structural design, and performance optimization of shock-absorbing wood materials.

Method Cunninghamia lanceolata (softwood) and Ochroma pyramidale (hardwood), both with a density of 0.335 g/cm³, were selected as experimental materials. Mercury intrusion porosimetry and microscopic observation were employed to characterize their hierarchical pore structures and anatomical features. Quasi-static compression tests were conducted along longitudinal and transverse grain directions to obtain stress–strain curves and calculate energy absorption and mechanical parameters. Additionally, a 3D ultra-depth-of-field microscopy system was used to dynamically observe microstructural failure evolution and morphological changes during compression.

Result (1) Despite similar densities and total porosities, significant differences in cellular structure and pore distribution across multiple scales were observed. Cunninghamia lanceolata consisted predominantly of tracheids ( ~ 95%), with gradual earlywood-to-latewood transition and rectangular or polygonal cross-sections; Ochroma pyramidale, a diffuse-porous hardwood, contained ~ 75% fibers with nearly regular hexagonal cross-sections. (2) Pore size analysis revealed that Cunninghamia lanceolata exhibited a broader pore size distribution with more macropores (Type II), whereas Ochroma pyramidale showed smaller, more concentrated pores and a higher proportion of micropores. (3) Mechanical testing indicated that under longitudinal compression, Ochroma pyramidale displayed a stable plateau phase, while Cunninghamia lanceolata exhibited pronounced stress collapse. Under transverse compression, both species showed monotonic “strain hardening” behavior, with Cunninghamia lanceolata demonstrating higher compressive strength. (4) Energy absorption analysis further demonstrated that Ochroma pyramidale performed better in longitudinal compression with smoother energy absorption, whereas Cunninghamia lanceolata excelled in transverse compression. These differences primarily stem from variations in cell morphology, material homogeneity, and chemical composition. (5) Failure morphology observations revealed that longitudinal compression induced through-cracks along rays and earlywood–latewood interfaces in Cunninghamia lanceolata, while Ochroma pyramidale maintained relatively intact structure. Under transverse compression, earlywood tracheids in Cunninghamia lanceolata and vessels in Ochroma pyramidale became the primary sites of deformation and failure.

Conclusion The microstructural pore architecture of wood decisively governs its compressive energy absorption behavior. At equal-density, Ochroma pyramidale achieves superior energy absorption capacity and stability in longitudinal compression due to its near-hexagonal fiber cross-sections, material uniformity, and abundant micropores. In contrast, Cunninghamia lanceolata exhibits better transverse energy absorption owing to minimal tracheid lumen diameter variation, graded earlywood–latewood distribution, and higher lignin content. Therefore, in practical engineering applications, wood selection should be guided by specific loading direction and cushioning requirements. This study elucidates the compressive energy absorption mechanisms of wood from a microstructural perspective, offering theoretical guidance for material selection and structural design in protective applications and providing insights for bio-inspired development of high-performance porous energy-absorbing materials.