A cast comprising a shell of bendable material with opposed ends and opposed edges, the shell being bent into a conical shape that is adapted to surround and form a gap with a part of a patient. The edges are fastened on and sealed to each other, and the cast includes a layer of casting material about the shell. A stretchable membrane is disposed in the gap and sealed on the shell forming a fluid tight bag which when inflated engages the patient's part. Metal particles on the membrane surface opposite the shell produce an oligodynamic effect.