Square foam blocks

Foams are two-phase material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material.^{: 6 : 4} The foam "may contain more or less liquid [or solid] according to circumstances",^: 6 although in the case of gas-liquid foams, the gas occupies most of the volume.^: 4 The word derives from the medieval German and otherwise obsolete veim, in reference to the "frothy head forming in the glass once the beer has been freshly poured" (cf.