A medical balloon includes at least one internal wall dividing the balloon into a plurality of separate chambers which may be separately inflatable and deflatable. The at least one internal wall is impregnated with heat conductive particles. The heat conductive particles enable heat produced during the balloon blowing process to pass through the polymer material of the balloon and specifically into the internal wall or walls, enabling these to soften and stretch during the process. This improves the integrity of the balloon and also balloon flexibility. The radiopaque particles embedded in the internal wall or walls of the balloon can also, in preferred embodiments, be of radiopaque material, providing the balloon with imaging visibility during deployment thereof in a patient.