A method of treating an elongated conductive element comprises exposing a conductive element sequentially to at least two dopants being different in composition. The dopants may include an acidic dopant and a halogen-based dopant. The conductive element comprises a plurality of carbon nanotubes and has a linear density in a range from about 0.1 tex to about 2.0 tex. The method further comprises mechanically densifying the conductive element. The elongated conductive element comprises at least one carbon nanotube fiber doped with a plurality of p-type dopants comprising at least one acidic dopant and at least one halogen-based dopant. The at least one carbon nanotube fiber has an electrical resistivity equal to or less than about 55 μΩ·cm and an ultimate tensile strength equal to or greater than about 1 GPa.