When the wood fibers that were sheared apart are hot-pressed into boards, lignin normally found in wood cells begins to flow. In a sense the wood fibers are coated by their own lignin. Brown rot fungus does not attack lignin. And many scientists believe that it is this fact that causes hardboard to be a little more resistant to decay than some untreated species like spruce, pine and fir. There are many similarities among the fiberboard products sold to builders.
Hardboard trim is readily available in all regions of the country.
All hardboard trim products weigh about the same, around 50 pounds per cubic foot. This is about twice as heavy as solid redwood. The motivating force for developing these products is cost and availability of high-grade solid wood . . . . Each of the manufacturers I talked with expressed concern over the reputation hardboard siding seems to have developed among builders. Thickness-swell is a problem.