Dynamics of a polydisperse 3D dry foam was experimentally investigated
by means of a novel nondestructive method, more precisely by optical
tomography associated to a foam reconstruction algorithm. The foam coa
rsening law obeys to a 3D extension of the classical von Neumann coars
ening law of 2D foams. It is obtained as [V-f](-1/3)d[V-f]/dt = k'(f -
[f]). [V-f] is the mean volume of f-faced bubbles, k' a diffusion con
stant equal to the single film gas diffusion coefficient, and [f] is t
he mean number of faces per bubble.