Foam

Foam is a two-phase material system of gas cells enclosed by liquid or solid material, made by the dispersion of gas in non-gaseous material. Foam "may contain more or less liquid [or solid] according to circumstances", although in the case of gas-liquid foams, the gas occupies most of the volume. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas.