ABSTRACT Face-layer density is widely known to be important for bending properties such as modulus of rupture (MOR), static bending Young’s modulus (Es), and dynamic bending Young’s modulus (Ed), whereas outer core-layer density is not. According to this study, the outer core-layer density is more important than face-layer density in commercial particleboard. Core and face layers were manufactured with coarse and fine particles, respectively. The coarse particles increased bending properties due to the presence of long wood fibers. However, fine particles did not increase the bending properties due to the absence of long wood fibers. Long wood fibers in the outer core layers, as opposed to the face layers, increase the bending properties. MOR can be predicted using Es (or Ed) and outer core-layer density. Furthermore, shear modulus (G) was determined, and the effects of layer density on G were investigated. However, they were not indicated.