A foam is a substance that is formed by trapping gas in bubbles. Gas is present in large amounts so it will be divided in gas bubbles separated by liquid regions which may form films, thinner and thinner when the liquid phase is drained out of the system. When the scale is small, e.g. for fine foam, this dispersed medium can be considered as a type of colloid.
- Lucassen, J. (1981). Lucassen-Reijnders, E. H. (ed.). Anionic Surfactants - Physical Chemistry of Surfactant Action. NY, USA: Marcel Dekker.