It is specially bonded ply wood, not sure what it's bonded with, to make it extra strong for deployment of goods by airdrop.
These particular ones where dropped in Afghanistan contained rough terrain motor cycles for the troops.
Typically there were so many crates dropped that they were able to build a compound from them so they double up as walls and roadways for reuse.
When a shipment needs to return home they simply rip a bit of road up, repack it send it home again.
Like all things they have a life and can only be used for a certain number of drops before being replaced hence I managed to get a quantity after their end of life.
These bits of wood have seen active service in a war zone so should be treated with respect your pen may well suffer from shell shock or could be a decorated war hero, give it a medal init?