In in Russia I saw a phone cable called "field cable" (провод полевой П-274-М). It is a loosely twisted pair with some iron strains added alongside with copper ones.
I tried to lookup something similar but I failed to find it. I used phrases like "field cable" and "military cable" but got nothing like that.
Such cable is really good to make a wire antennas on trees because it has teflon-like surface and tolerant against harsh environment.