In modeling the viscoelastic moduli of liquid foams undergoing small periodic strains, the foam is viewed as a continuum and the moduli are viewed as linearly proportional to the capillary pressure. An isotropic dodecahedron is chosen to represent "on the average" the basic microunit, and variational statements of nonlinear structural mechanics bring out the specific macromechanical properties of the foam under static and dynamic loading, in terms of the mechanical attributes of the films-surface tension and surface viscous dilatation.