  Liquid foams have been observed to behave like immersed granular materials in
at least one respect: deformation tends to raise their liquid contents, a
phenomenon called dilatancy. We present a geometrical interpretation thereof in
foams squeezed between two solid plates (2D GG foams), which contain pseudo
Plateau borders along the plates, and in 3D foams. While experimental
observations evidenced the effect of a continuous deformation rate (dynamic
dilatancy), the present argument applies primarily to elastic deformation
(static dilatancy). We show that the negative dilatancy predicted by Weaire and
Hutzler (Phil. Mag. 83 (2003) 2747) at very low liquid fractions is specific to
ideal 2D foams and should not be observed in the dry limit of real 2D foams.
