This is the genuine JSC American DR-450S 450 Ohm Low Loss Ladder Feeder Cable, in 10m lengths (multiple listing,  so order what you need)

It is much easier to handle than traditional open wire feeder yet retains the ultra low loss feature. The conductors are #18 copper-clad, spaced 22mm. This feedline will handle 1kW with ease and is far superior to the common 300 Ohm ribbon type.