What is the best copper for mains cables ?

Select-Hifi I am currently trying to source cable for my own DIY job based on https://www.tnt-audio.com/clinica/ttse.html
Amazing how expensive cable is and European suppliers mostly sell full reels at many hundreds of euro upwards.   For availability reasons I'll probably get a cable made by Lapp.   Lapp Olflex classic 100 CY.   Belden do a quality copper  screened Teflon insulated cable 83702 or 83321E which is available cut in the US.
The link I gave uses an earthed screen with a full regular cable for each indepent live, neutral and earth core.  They are plaited too.   Very easy to make also. 

Cost is tiny and whilst I am a total sceptic on cable hype, the cost means I'm going to try it and see.   Sourcing issues mean I have to buy material for 5 but still so cheap that it's worth the risk. 

Screened copper cable for IT is designed with screening and material designed to eliminate interference and loss of signal quality. e.g. Belden. Probably will be shot down for suggesting it but a fraction of the price of Audio cables.   

As suggested elsewhere I doubt the audio companies draw their own wire and extrude their own insulation.  What do they use? and who do they buy their raw material off? 

European Kettles use IEC connectors very similar to standard IEC (C13 I think) connectors used on audio equipment hence we use kettle lead term a lot.