OSB is a multi-layered wood-based composite. The individual layers consist of long slender wood strands bonded by a polymeric adhesive. The strands in the surface layers are oriented in the major axis of the board. The high aspect ratio of the strands (length to width 10:1) increases the board's bending strength in the direction of the strand. Strands in the core layer can be distributed randomly but generally they are aligned perpendicular to the grain of the surface layer (minor axis).