Sitting here looking at the stock Senn HD280 coiled cord and wondering how it was made. Do they take the fully made cable then coil it or do they coil the wire first before applying the insulation? The surface of the cable on the inside of the coil is flat, while the uncoiled part is completely round, don't know what that might mean just an observation. I would guess they apply the insulation while coiled cause it just wants to hold it's shape way too well to have had the coiling done on the finished cable. Anyone?
Actually, a special type of spiral insulation/jacket combo is applied to cables to make them retract or coil up. Loosely-coiling retractile cables just use the special spiral insulation/jacket, while tightly-coiling retractile cables have a spiral wire shielding (in addition to the special insulation/jacket) that give them more springiness.
Flat or half-round wire are used in the coiled section because they're easier to coil and resist straightening out once they've been coiled, whereas round wire is resistant to coiling in the first place and tries to uncoil when at rest.