Physical methods have been used to compare the mechanical properties of wood based panel products in relation to their microstructure. Three types of composites were considered: medium density fiberboard (MDF), oriented strandboard (OSB) and chipboard (CB). The overall elastic properties of panels were assumed to be orthotropic. The diagonal terms of stiffness matrix were determined with ultrasonic velocity method. The properties of the skin and the core of the panel were characterized using X-ray microdensitometry, ultrasonic velocity measurements, dynamic thermo-mechanical analysis (DMTA) and low voltage scanning electron microscopy (LVESEM). Clear differences have been established in the physical properties of the three panel products. Average mechanical properties have shown that the highest anisotropy is in OSB and the lowest in CB. Always the mechanical characteristics of the skin are higher than average characteristics of the panels while that of the core are inferior to average characteristics. E elastic modulus is much more higher (2 to 5 times) in the skin than in the core. X-ray microdensitometric technique has shown that the heterogeneity in the skin and core is the highest in OSB.