ORIENTED STRAND BOARD. Wood strands bonded with adhesives to form a mat. Like the veneer in plywood, these mats are layered and oriented for maximum strength, stiffness and stability. The individual strands are typically three to four inches long. OSB is widely used as construction sheathing, as the web material for wood I-joists, as the structural skins of structural insulated panels (SIPs), and in a growing number of other applications.