A method of forming a tubular body for a catheter, sheath or lead comprises extruding a polymer core having an integrally formed core wall, first lumen, and second lumen, placing a first layer over an outer circumferential surface of the extruded polymer core, and bonding the first layer to the circumferential surface of the extruded polymer cover via a reflow process. The first and second lumens are mandrel free during the reflow process, and a temperature of the reflow process is below a softening point of the polymer core to maintain a collapse free first and second lumen.