Asphalt board consists of wood fibers that are soaked and compressed under low pressure and high heat. The board is porous and impregnated with asphalt to increase moisture resistance. As a rule, no additives of glue are needed, but the wood's natural lignin binds the fibers together.
 Asphalt board is open to diffusion and the impregnation increases not only the moisture resistance but also the resistance of the board to mold, rot and
 pest infestation.