Plywood is a manufactured wood which is made by gluing several thin sheets of wood together with the grain alternately running along the sheet then across it.
The veneer is usually about 3 millimetres thick for each layer. Interior layers of these boards are usually made from an inexpensive wood while the outer veneer layers are made from more expensive timber to give the board a nice wood grain appearance. The glued layers are heated together to make the seal become better bonded.