What is this plastic sheet used for?

I just bought a pickup truck, and it has this large 4'x8' plastic sheet in the back. Its about an inch thick, and weighs a LOT. It has nothing to do with a bed liner or anything. It seems to be extremely durable, from being in the back of a work truck for over 10 years its just got some scratches. Does anyone know what it could be used for? I want to try and sell it, but I have absolutely no idea what its purpose is, so I dont know how to even list it! One of my friends suggested it may be used for flooring or something, but i have no idea. I could see it being cut up and used for bench tops or something of that sort, but again, no clue. Any ideas?What is this plastic sheet used for?
It probably was used as a bed liner, the rest of us just use a sheet of plywood and this guy had access to the plastic sheeting, so used that insteadWhat is this plastic sheet used for?
MY GUESS IS THAT IT IS ANTI FATIGUE MAT USED ON FACTORY FLOORS IN FRONT OF MACHINES..THEY ONLY SELL FOR $39 NEW AT TRACTOR SUPPLY STORES