a unitary , flexible , substantially noncollapsible catheter tube of biocompatible material is comprised of hard and soft regions . the hard regions can be ring shaped or helical . the hard regions provide sufficient rigidity to the tube to prevent collapse under normal usage as the interior and exterior pressures vary . the soft regions provide sufficient flexibility to allow contoured placement of the tube . the hard regions can be created by exposing a polymer in the tube to radiation . the hard regions can also be created by periodically adding a harder material to the tube .