A tearaway introducer sheath assembly (10) for use in implantation of a catheter into a patient, having an elongated polytetrafluoroethylene sheath tube (12) and a proximal polyethylene hub component (16). The hub comprises two halves (22) insert molded about the sheath tube proximal end and joined to each other by frangible webs (28) enabling manual splitting. At least one pair of opposed holes (42) is formed through the tube proximal end portion 44, and a polyethylene liner (46) is inserted into the tube's proximal end portion. The polyethylene flows into the at least one pair of holes (42) to fuse with the liner, establishing a pair of physical joints (50′) integrally joining the liner (46) to a respective hub half (22). Upon manual splitting of the hub halves, the sheath tube easily splits along its length as a result of a property of the polytetrafluoroethylene material.