The actual insulation around the wire itself is Teflon... I think the blue outer sleeve is PVC.Not from my experience. The outer jacket is Teflon and the insulation around the wire is PVC. It is the outer jacket of the cable that is plenum rated.
In the case of Belden they stopped using Teflon for the outer jacket of their plenum rated cable years ago. Belden developed their own outer jacket material. It is called Flamarrest®.
Outer Jacket Trade Name Outer Jacket Material
Flamarrest® LS PVC - Low Smoke Polyvinyl Chloride
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That said, this was just meant to be an experiment to see what I think about multiple solid gauge conductors, separately insulated and braided together to form larger conductors. I’ll probably do something similar out of 20 or 18 gauge 600v wire. Any recommendations? OCC or the like would be nice.
There are quite a few cable company manufactures that make after market power cords for audio equipment that use multiple paralleled individually insulated solid core wire for each of the two current carrying conductors of their cords.
Examples of aftermarket power cords using multiple insulated solid core conductors.
PS Audio
http://www.audioadvisor.com/prodinfo.asp?number=PSPWAC5
Pangea Audio AC 9SE MKII Signature Power Cable
http://www.audioadvisor.com/prodinfo.asp?number=PGAC9S2
Audioquest
https://www.crutchfield.com/S-wi4RnpruA6y/p_703NRG23F/AudioQuest-NRG-2-3-ft.html
Shunyata
METALS AND CONDUCTORSCCC
- COMPUTER CONTROLLED CRYOGENICSPROPRIETARY PROCESSESVTX™
ConductorsShunyata Research’s exclusive VTX™ conductors are made in the shape of virtual tubes. The core of the conductor is completely hollow minimizing skin effects and random eddy currents. They are produced using OFE Alloy-101
http://www.shunyata.com/images/technical_features/pdfs/pwr_tech_201509.pdf
Not sure of their actual construction design. I couldn’t find any actual pictures.
Note in all cases the outer protective insulation covering the hot and neutral conductors/wires is PVC and rated for mains power handling applications.