That stuff was used during the war because of material shortages, maybe some of it was left after the war. I've never seen that stuff in person, I only read it was quite common in Northern Germany where most houses mainly consist of straw... ugly!
The only wartime wire I've ever seen is old conduit wire, looks like the standard cloth covered wire but at a closer look there is no cloth... only the most brittle rubber I've ever seen! There were such rubber wires with much older cloth wires in one and the same conduit, the rubber stuff crumbled the instant I touched it and the cloth wire was still like new. I think aluminum wire was also a deal during war because they needed the copper for ammunition. Supposedly they also used some weird iron alloy named "new silver" for stranded wire back then... it's extremely springy and a bear to work with. I once saw it on an old radio.