A method for making a flexible, kink-resistant medical tube having a body and a lumen, the method comprising: providing a die body (102, 1930) defining an internal cavity having an inlet side and an outlet side; providing a die pin (104, 1932) received within the internal cavity of the die body (102, 1930) such that a die flow channel is defined between an outer surface of the die pin (104, 1932) and an inner surface of the die body (102, 1930); providing a first liquid polymer material to the inlet side of the die body (102, 1930); providing a second liquid polymer material to the inlet side of the die body (102, 1930), which step of providing the second liquid polymer material comprises supplying the second liquid polymer material to at least three distinct locations before the inlet side of the die body (102, 1930); extruding the flexible tube by flowing liquid polymer through the flow channel from the inlet side toward the outlet side of the die body (102, 1930), wherein the first liquid polymer material forms the body of the tube; and inducing a helical rotational flow of the liquid polymer material as the liquid polymer material flows through the flow channel; wherein the helical rotational flow creates a helical structure (1970, 1972, 1974) within the body of the tube, which helical structure (1970, 1972, 1974) comprises at least three helically oriented segments (1970, 1972, 1974) extending longitudinally along the body of the tube, wherein the helically oriented segments (1970, 1972, 1974) are formed of the second liquid polymer material, which helical structure resists formation of kinks along the body of the tube, and wherein the helical rotational flow is induced by at least three helical grooves (122, 1936), formed in the outer surface of the die pin (104, 1932), wherein helical rotational flow is further induced by rotating an insert rotatably coupled to the die body (102, 1930) that surrounds the die flow channel to set a rate of twist of the helical structure relative to a radial distance from the lumen of the tube, and. wherein an inner surface of said insert forms the outer surface of the die channel and is located at the outlet side of the die body (102, 1930). providing a die body (102, 1930) defining an internal cavity having an inlet side and an outlet side; providing a die pin (104, 1932) received within the internal cavity of the die body (102, 1930) such that a die flow channel is defined between an outer surface of the die pin (104, 1932) and an inner surface of the die body (102, 1930); providing a first liquid polymer material to the inlet side of the die body (102, 1930); providing a second liquid polymer material to the inlet side of the die body (102, 1930), which step of providing the second liquid polymer material comprises supplying the second liquid polymer material to at least three distinct locations before the inlet side of the die body (102, 1930); extruding the flexible tube by flowing liquid polymer through the flow channel from the inlet side toward the outlet side of the die body (102, 1930), wherein the first liquid polymer material forms the body of the tube; and inducing a helical rotational flow of the liquid polymer material as the liquid polymer material flows through the flow channel; wherein the helical rotational flow creates a helical structure (1970, 1972, 1974) within the body of the tube, which helical structure (1970, 1972, 1974) comprises at least three helically oriented segments (1970, 1972, 1974) extending longitudinally along the body of the tube, wherein the helically oriented segments (1970, 1972, 1974) are formed of the second liquid polymer material, which helical structure resists formation of kinks along the body of the tube, and wherein the helical rotational flow is induced by at least three helical grooves (122, 1936), formed in the outer surface of the die pin (104, 1932), wherein helical rotational flow is further induced by rotating an insert rotatably coupled to the die body (102, 1930) that surrounds the die flow channel to set a rate of twist of the helical structure relative to a radial distance from the lumen of the tube, and. wherein an inner surface of said insert forms the outer surface of the die channel and is located at the outlet side of the die body (102, 1930).