Absorption, and particularly wavelength selective absorption is an important factor in the function of the filters. The two most commonly used absorbers are thin metallic films which are particularly insensitive to wavelength for absorption, and colored glasses which absorb wavelengths varied by as much as several orders of magnitudes in only tens of nanometers. Interference filters are multilayer dielectric thin film devices. Metallic films, colored glasses and thin dielectric films are used in CNI filters.