To simplify this, it is like putting a varnish over the ink after your mail piece is printed at the printer. It speeds up their drying time and, in some cases, gives it a high gloss finish. We DO NOT recommend your mail piece come to us coated, because the ink used for addresses has a much harder time adhering to this surface. In some cases we have to apply labels instead of inkjet. Request that the coating be left off on the mail side when you talk to your printer.