Coating is the application of a layer to a substrate. In general, in order for a thin uniform layer to be applied, the application must be done at low or moderate viscosities. In many cases this low viscosity is achieved by dissolving or dispersing the desired coating in a liquid such as water or a solvent, but this then necessitates the subsequent removal of the liquid by, for instance, a drying process. Hot-melt coating achieves this low to moderate viscosity by melting the desired material before applying it to the substrate. The substrate and coated layer are then cooled, generally by passing over a chilled roller. There is no liquid to remove, so the process is, in principle, much faster than water- or solvent-based equivalents. ==Terminology & use==