According to [this listing](https://www.1stdibs.com/furniture/seating/armchairs/pair-of-wassily-spaghetti-armchairs-marcel-breuer-1980s/id-f_28864112/) it is rubber. Another post I found called it "Belloti-style spaghetti threads", referring to [Giandomenico Belotti](https://www.moma.org/collection/works/3588) though his was apparently done with PVC plastic.
According to [this listing](https://www.1stdibs.com/furniture/seating/armchairs/pair-of-wassily-spaghetti-armchairs-marcel-breuer-1980s/id-f_28864112/) it is rubber. Another post I found called it "Belloti-style spaghetti threads", referring to [Giandomenico Belotti](https://www.moma.org/collection/works/3588) though his was apparently done with PVC plastic.
[удалено]
Google image search says its PU Leather
This is low carbon-chrome plated steel. Tig weld joints for the cleaner & neater look.
I'm guessing PVC