What is the best copper for mains cables ?

select-hifi writes:

I took the pluge and went for 3 x 2M lengths of Nanotec 308 with Furutech NCF connectors, I must say on very few hours i am really pleased with my choice....the sound is already to my ears a step up from the kettle leads that came with the equipment...
... I paid $99 for 1M and various prices for the Furutech NCF range UK plugs and connectors.

Kettle leads, eh? Never heard them called that before. We just called em patch cords back in the day. Whatever. Shakespeare said A rose by any name would smell as sweet. I say a patch cord by any name would sound as crappy. Whatever you call it, free is a pretty low standard. Go buy whatever $100 will get you in Synergistic Research. Not even the $150 you spent including the connectors, just the $100 you spent on the wire. My guess is you'll be surprised how much better it is even for less than you spent.

A reasonable, if irrelevant, question.

Of course nobody makes their own wire. Nor do they make their own dielectric, nor the mesh wrapper. I seriously doubt any of them even makes their own terminals, plugs or sockets. It's simply way too inefficient, costly and counterproductive. Oh a few things here and there. You need to experiment and that at some point involves making something never made before. But even then, once you know what you need, its almost always more efficient to go to a manufacturer and have them make it to your spec. Because that level of manufacturing skill is not where the expertise that matters is anyway.

Way back in the early 1990's Ted Denney III told me he noticed the reels of wire made to his spec did not sound the same. Drilling down he had to learn a lot about how the wire was made, to eventually discover what is basically like the peanut allergy problem. Those signs warning "equipment used to process peanuts"? Because even a tiny amount can be a problem for some people. Well the same equipment is used to process different metals. The numbers we pay so much (way too much) attention to say how many nine's there are of copper, but say nothing about what the 0.001 is. What Ted figured out is that tiny trace actually makes a difference.

Ted did not find this out by testing. His supplier swore everything was to spec. Passed all the tests. Precision product. Only Ted with his ears could hear the difference. Some things you would never know or learn any other way than by listening. 
 
That is why all these debates bore me to tears. Total waste of time. Worse than a waste, because it distracts from time being spent on something productive, like what does it sound like? Yet it is what the vast majority keeps wanting to talk about.

Its just nonsense. The question of what is the right copper is really only one question out of dozens. What is the best wire diameter? How many strands? In what configuration? What is the best geometry? What is the best insulator? What is the best termination? What is the best way of fastening the wire to the terminal? On and on.

None of which is answered any way other than by listening. Nothing else matters. 

J Gordon Holt introduced listening as the evaluation standard more than 50 years ago. Would've thought it'd have caught on more by now. Oh well.