The intrinsic hiding power of a paint is described very well by the Kubelka-Munk theory, which yields a number that is often called the theoretical spread rate. This expresses the number of square metres of a wall that can be covered at a certain contrast ratio. The underlying test method assumes highly uniform application, a condition which can be met under lab conditions but does not necessarily match the hiding power of a coat of paint applied with a roller. To an extent depending on the paint's flow characteristics, the substrate, the type of roller, etc, the roller creates a ...