Thin films can be solid or liquid (gaseous is rare). The thin film's composition, structure and properties may differ from those of the bulk phase the thin film originates from. Solid thin films are oxide films on the metal surface and synthetic film coatings formed on various materials to create microelectronic devices, prevent corrosion, improve the look and so on.

Liquid thin films are divided into the gaseous dispersed phase in foams and the liquid phase in emulsions; stable foams and emulsions are possible only if surfactants are present in the films. Liquid thin films can evolve spontaneously between the grains in polycrystalline solids, if the grain boundary surface energy is more than twice as high as the solid-liquid interface tension (Gibbs-Smith condition). Gaseous thin films with a notable lifetime may arise between a droplet and bulk liquid during evaporation.

To determine the thickness of thin films, techniques are often used based on measuring the reflected light intensity using ellipsometry, for instance; electrical methods are also used based on measuring thin films’ capacity and conductivity. To study solid thin films, electron microscopy, X-ray spectroscopy and other techniques are used designed to analyse surfaces of solids. Thin films and thin film coatings form the basis for some modern fields of technology, especially microelectronics.