Loaded objects on board of the ship are not always completely flat. After the cribbing beams are installed according to the plan, sheet material (plywood) is/can be added on top of the beam to ensure that the cargo is optimal supported. These strips plywood material are custom sawn and sorted nicely on thickness.
What kind of plywood is to be used depends on your wishes in engineering. The bonding of the sheet material are always "exterior" and are delivered as much as possible with the FSC® or PEFC™ mark