In traditional mechanics of materials, the stiffness of a beam or plate in bending is described by its cross-sectional shape as well as its material properties, primarily the modulus of elasticity. Previous work at the USDA Forest Products Laboratory, Madison, Wisconsin, has shown that modulus of elasticity has a strong correlation to the density of the fiberboard. Examined here are experimental and theoretical relationships between process variables of bulk density and area density and the transverse bending stiffness of the fiberboard. A model is developed and evaluated for the relationship between area density, bulk density, and bending stiffness.