[faileas]

I've been wondering this a while- unless you have absolute bargain basement headphones (i've seen ones which had 2 single strands per earpiece... granted these were free with the incredibly cheap and nearly useless 32 mb mp3 player i use when testing connections), your ground and signal cable 'bundles' have their own insulation from each other- so why exactly does multistranded headphone cables have each strand covered by a coating? I'd note most DIY cables don't seem to have this, and they don't actually lose out in terms of SQ from what i can tell but this seems damned near universal.

 

[haloxt]

http://en.wikipedia.org/wiki/Litz_wire

 

[nikongod]

Its not Litz wire, not intentionally anyways.
 
The strands are individually coated because its less expensive to have 10 individually coated strands with no "thick" insulator around all of them than to have 10 uncoated strands with a proper "thick insulator". If you look at the really cheap headphone cables, they rarely have all of the strands of a particular conductor in its own insulator. 
 
In nicer wires "litz wire" does apply 

 

[weibby]

insulation takes up space and hard to fit such a thick cable onto a headphone.
IMHO to lighten up the load yet serve its practicality, litz is used within a single insulation for ground.