This study comparatively investigates the in-plane compressive properties of 3D braided honeycomb composite core (3D-BHC) and 3D braided honeycomb-foam sandwich composite (3D-BHFSC). The effects of joint wall length on mechanical properties, energy absorption, and failure mechanisms were analyzed using quasi-static compression tests and 3D digital image correlation (3D-DIC). The results show that the maximum load and energy absorption of 3D-BHFSC increase with the number of free wall columns, while the failure displacement is primarily governed by free wall rows number. The addition of foam filling and face sheets to form sandwich structure (3D-BHFSC) significantly enhances structural performance: the maximum load approximately doubles compared with that of 3D-BHC, energy absorption improves by 1.7–1.8 times, and the in-plane compressive modulus rises by about 500 MPa. However, 3D-BHFSC exhibit reduced failure strains and displacements due to progressive damage accumulation. Strain-field analysis reveals shear-dominated failure modes in 3D-BHC, evolving into V-shaped or cross-shaped fractures in 3D-BHFSC. These findings unravel the interplay between honeycomb topology and sandwich performance and provide quantitative guidance for designing lightweight sandwich structures in aerospace, automotive, and defense applications. ... Read more