If you look closer, you'll probably find only the outer protective layers are cloth; I've seen that on a lot of older wiring, but the ones I have seen all had a thin inner layer of rubber right on the copper. Tarred cloth probably would work, as long as the voltages were low enough and there were multiple layers; paper might be even better though. (Most of the old wiring I have seen was a thin layer of rubber next to the copper, then paper wrapping protecting the rubber and separating the individual wires, and the whole bundle protected with fabric.)