Abstract
Recent observations have suggested a revision of the prevailing view that monodisperse foams are generally disordered. Among the ordered structures which are possible, b.c.c. (the Kelvin structure) should prevail at low liquid fractions, and f.c.c. (or other close-packed structure) at high liquid fractions. The instabilities of both structures are discussed, and it is argued that structures of the clathrate type should intervene in the intermediate range. This scenario offers an interesting challenge to further experiment (including emulsions) and computation.