Insulating board is a rigid or semi-rigid synthetic product commonly referred to as structural insulating board, rigid board, sheathing board, and produced under a variety of tradenames. It is available in 1/2 to 1 inch thicknesses, and in board sizes generally 4ft. by 8 ft. Some insulating board is produced specifically for use on interior walls. This type is generally made from wood fibers, and one side is prefinished. Insulating board designed for use as structural insulation is produced from compressed fibrous materials other than wood and does not have a prefinished surface.