A foam generating device for generating therapeutic foam is provided comprising: a) a sealed chamber of variable volume and having a wall, the chamber containing foamable liquid and gas and having a predetermined initial volume and b) a foam generating structure located within the chamber； whereby a therapeutic foam may be generated by circulating the gas and liquid through the foam generating structure within the chamber； characterised in that at least one part of the wall of the chamber is of flexible or compressible material, such that on extraction of therapeutic foam from the chamber, the chamber is capable of reversibly reducing its volume by 20% or more from the said predetermined initial volume, without substantial change in pressure, whilst still permitting circulation of gas and liquid to maintain the remaining foam in the chamber.
