Machining qualities of edges and surfaces. Reduce weight, resulting in lower handling and shipping costs. Reduce manufacturing costs on hard-boards of equal caliper. Less fiber and resin are required. Improve nailing and stapling.
Specific gravity is the ratio of the density of a material compared to the density of water.
The density of hardboard is usually given as specific gravity for convenience of comparison with other materials. Because of its density hardboard is harder than most natural wood and because of its grainless character it has nearly equal properties in all directions in the plane of the board. It is not so stiff nor as strong as natural wood along the grain, but it is substantially stronger and stiffer than wood across the grain. Modulus of rupture, the ultimate unit strength of a material in flexure or bending, has become a common measurement of hardboard strength. Even though the figure obtained is not mathematically correct, it is valuable in that it combines tensile, compressive and bending properties.