<p>Balsa wood (<i>Ochroma pyramidale</i>), known for its low density, renewability, and inherently anisotropic cellular structure, is a promising natural candidate for vacuum insulation panel (VIP) core materials. This study systematically investigates the effects of density variation (70-190 kg·m^-3) on the microstructural characteristics, mechanical properties, and thermal behavior of balsa wood, aiming to establish comprehensive structure-property-performance relationships. SEM and optical microscopy analyses reveal that increasing wood density significantly reduces porosity and thickens cell walls, resulting in pronounced enhancements in compressive strength (longitudinally from 3.04 to 11.40 MPa) and thermal stability (with peak decomposition temperature rising from 311.03°C to 345.24°C). Mercury intrusion porosimetry confirms these structural changes, showing a reduction in total porosity from 89.6% to 61.1% and a corresponding narrowing of pore size distribution. Thermal conductivity tests indicate marked directional dependence, where longitudinal conductivity consistently surpasses radial and tangential values, highlighting the crucial role of fiber orientation in heat transfer mechanisms. Upon vacuum encapsulation, thermal conductivity decreases by over 70%, achieving a minimum of 9.88 mW·(m·K)^-1 in the tangential direction at the lowest density tested (70 kg·m^-3), effectively demonstrating the suppression of gaseous conduction. These findings underscore that strategically density-controlled and directionally optimized balsa wood can serve as a high-performance, eco-friendly core material for VIPs, offering significant potential in advancing energy-efficient and sustainable building technologies.</p>