Possible Duplicate:
Why aren't solenoid/electromagnet windings insulated?
Looking at some pictures of inductors, such as this one:
(source: ddmcdn.com)
The wires don't seem to be covered with a layer that prevents current from simply flowing from one wire to the next, all the way down. What keeps the electric current going in loops, rather than just flowing straight down the coil and producing no magnetic field?