compo board
Insulating board, hard board, building board – loose terms for a sheet product of vegetable fibers mechanically or chemically formed into a pulp, rolled, and pressed; in some cases a binding material or chemicals have been added to provide resistance to moisture, fire, rodents, etc. These sheet products are widely used as a sheathing, lath, insulation, and interior wall surfacing. (Saylor, 1952)