A catheter (40) or sheath (14) is provided with a strengthening element (30) embedded within the walls of the catheter (40). The strengthening element (30) is formed of a plurality of short strengthening members (32) arranged in longitudinally overlapping manner but which are radially spaced from one another and fixed to one another by annular coupling elements (36). The strengthening element (32) is made of a metal or metallic material, whereas the coupling elements (36) are made of a non-conductive material. The coupling elements (36) prevent electrical conduction through the length of the catheter (40) but retain a strengthening structure which provides torque strength and kink resistance. The short sections of conductive strengthening members (32) provide shielding of electromagnetic waves but prevent the strengthening element (30) acting as an aerial.
