The deposited film is typically very thin, and composed of small platelets formed when the vapor hits the substrate. Films are usually in the neighborhood of 1000 angstroms thick. Films may contain small pinholes. Films are generally fragile and should be protected with a topcoat. There are exceptions to this, like SiO films. Films take on the character of the substrate underneath. Reflective films must have a smooth substrate. Film thickness can affect opacity, color and reflectivity.