Interconnects: solid or hollow core wire?

I know what solid core is. I know what stranded is. I do not know what hollow core wire is? Isn't wire by definition solid as even stranded is made up of small solid core? Is there an audio cable that uses metal tubing?

Mrtennis - I think TNT Audio has some solid vs. stranded theory on the website and is the basis for some of their DIY cables.

http://tnt-audio.com/clinica/spkcbl_e.html

That's the problem with cables, it's impossible to make comparisons with all other things being equal.

The biggest factor that should be made identical in a comparison is resistance, but that would require custom lengths to make perfect matches.