slide on wire insulation?

Hi, I'm doing some delicate rewiring inside some ancient aviation simulator equipment. For the shorter soldered connections, the original manufacturer used thin, bare solid wire, but had slid some kind of strong, clear insulation over each wire, to keep the bare wire from touching other wires. Kind of like heat shrink tubing, but thicker, and not heat-shrinkable. I had to discard some of this slide-on insulation, in the process of rewiring the ends of a few wires, and I'm wondering where I can find more of it. I've been trying to search for it on the Internet, but all the comes up is either heat-shrink tubing, or the huge sleeves for protecting bundles of wires. Heat shrink tubing what not be ideal as I'd have to put a lot of heat down into thick messes of wires. Does somebody know the name of what I'm looking for, and where I could order it?