A paper cup is a cup made out of paper and often lined with plastic or wax to prevent liquid from leaking out or soaking through the paper. The base paper for paper cups are called "cup board" and are made on special multi ply paper machines and have a barrier coating for waterproofing. The paper needs high stiffness and strong wet sizing. The cup board grades have a special design for the cup manufacturing processes. The mouth roll forming process requires good elongation properties of the board and the plastic coating.