8 this composite inner layer 9 which forms the inner container 3 is non permeable to at least the saline solution filler material 4 of the prosthesis 1 and body fluids of the recipient of the prosthesis 1 the inner layer 3 is effective in limiting the passage of the saline solution 3 from the prosthesis 1 to the body of a recipient thereof it also limits the ingress of body fluids from the recipient into the prosthesis 1 the inner layer 3 therefore acts as an osmotic barrier which reduces the osmotic driving force which seeks to balance the concentrations of solutes on opposite sides of the barrier in this case the shell 2 of the prosthesis 1 it is also possible to construct the inner and outer containers of a prosthesis according to a second embodiment in this second embodiment of a prosthesis according to the invention shown in fig3 the prosthesis not shown includes a filler material in the form of a polyvinyl pyrrolidone pvp based fluid not shown the pvp is a water soluble polymer and is hydrophilic which means that it easily bonds with water by means of a hydrogen bond in this way the pvp is easily dissolved in water to form the filler material for this embodiment the inner container 10 is formed by the inner layer 11 which comprises polyethylene the pvp based fluid does not move through the polyethylene inner layer 11 under force of osmosis and the inner.