Insulated Hookup Wire: Plastic Over-Jacketed onto Copper

Insulated wire is made by over-jacketing extrusion, the usual way to insulate wire: copper wire is pulled through a die while an extruder pushes molten plastic around it. The extruder melts plastic pellets with a turning screw and heaters along its barrel and pushes the melt through a screen pack into the die. With jacketing tooling the melt meets the wire only just before the die lips; with pressure tooling it meets the wire earlier, under high pressure, so the insulation grips the wire. The coated wire is pulled through a water bath to cool, because plastic gives up its heat slowly.