Cups for cold drinks could not be treated in the same way, as condensation forms on the outside, then soaks into the board, making the cup unstable. To remedy this, cup manufacturers developed the technique of spraying both the inside and outside of the cup with wax. Clay- and wax-coated cups disappeared with the invention of polyethylene (PE)-coated cups; this process covers the surface of the board with a very thin layer of PE, waterproofing the board and welding the seams together.