Here are at least 18 different types of wire insulation: polyurethanes, nylons, poly-nylons, polyester, and to name a few. Pickup makers have learned how to use different types of insulation to refine a pickup’s tonal response. For example, a wire with heavier insulation can be used to maintain more high-end detail.
Period-accurate wire is used in all vintage-style pickups. One popular vintage-style insulation is Formvar, which was used on old Strats and on some Jazz Bass pickups. But what the insulation vintage buffs know best is plain enamel, with its blackish-purple coating. Plain enamel wire was common in the ’50s and into the ’60s before the new insulations had been invented.