A foam is a dispersion in which a gas is dispersed in a liquid or solid. The foam and soap foam when the beer is opened are all foams of the gas in the liquid; the bubbles in the foam and the foam glass are the bubbles of the gas in the solid, and the solid foam is a light porous sponge-like substance or a lightweight porous rigid substance. .
For gas/liquid dispersion systems, when the bubbles are separated by a thicker liquid film and are spherical, the foam is called a spherical foam, just like an emulsion in which the internal phase is a gas. However, in general, the volume fraction of the gas as the dispersed phase is very high, the gas is separated by a network of liquid films, and the bubbles surrounded by the liquid film are deformed into polyhedrons in order to maintain pressure balance. This foam is called a polyhedral foam. . Polyhedral foams are commonly referred to as foams in gas/liquid systems that can be self-generated by the spheroidal foam by sufficient drainage. In order to maintain mechanical stability, they always intersect in a certain way, for example, when three bubbles intersect at 120°, they are most stable.