In my recent quest for 4 conductor right angle connector cables, I received some small diameter, very flexible cable assemblies.
The first cable I cut for a custom application had many very fine, round stranded (not flat foil) spiral wound around a synthetic thread with each individual strand coated (not jacketed) with a thin colored coating. No other insulation or shielding was found.
This highly flexible wire is what I've been finding lately in cheap headsets and earbuds. The separate conductors are bundled together in a molded/extruded plastic jacket with different colored coatings on each conductor.
I'd read that paint stripper would remove the colored coating/insulator, so that was tried.. after 15-20 minutes some of the coating could be removed by wiping the ends with a cotton swab. Additional stripper was applied and set aside for over a half-hour.. the stripper had become colored by the dissolved coating, and wiped of very cleanly.
I wound some 30ga wirewrap around the ends to form an improvised strain relief for the fine bundles, then placed this cable aside to try a different method.
On another section of the same cable, I placed the bundled ends on a scrap of clean wood and just wiped the dry tip of my soldering iron several times along the bundles, moving toward the ends. The heat was effective at removing the colored coatings from the bundles.. turning the cable over to get the ends thoroughly cleaned to the bare copper.
The bundles were then individually covered with the smallest heatshrink tubing (maybe 1/64" dia) with the bare ends left exposed. The 4 sections of small shrinktubing were joined together and to the plastic cable jacket with a larger diameter section of shrinktubing (over a very small amount of hot glue applied to the junction area).
The wirewrap treated ends would've been problematic for this particular application since the 4 cable leads needed to be soldered to tiny terminals that fit in a nylon connector. The shrink tubing needed to be gripped/secured by the terminal tabs intended to be crimped to/imbedded in a plastic insulation for added strength.
With the approx 1/32" bare ends soldered to the terminals and the tabs securing the shrinktubing, the connection was fairly secure. For additional strength a small amount of hot glue was applied to the short lengths of heatshrink tubing entering the connector body, followed by another section of larger heatshring tubing to cover all, effectively making an improvised molded cable end connection/strain relief.
I like a better quality cable for these assemblies, but I wasn't able to find right angle TRRS plugs in 2.5 and 3.5mm sizes. The cable which as been working well for me is Mogami type 2929.. an ultraflexible miniature 28ga (fine stranded copper) 4-conductor (plus a spiral-wound copper shield) with an outer diameter of ~0.110".