What is the best dielectric?


A vacuum is the best dielectric? Since this is not pratical would air be the next best dielectric or would there be a better sounding dielectric like cotton?
Would there be a difference for speaker wire or interconnects?
Thanks
cdc
Some reasons to admire a design such as Anti Cables are (1) no dielectric, (2) no jacket, (3) no shielding, (4) high purity copper and last but not least, (5) directional ARROWS.  
No dielectric is the best dielectric.

That said, air would be my weapon of choice. 
Like @kijanki has said, an ovesized Teflon jacket is among the best. My  Tempo Electric speaker cables are one piece, solid core 14 gauge silver with a 9 gauge Teflon sleeve. Air becomes the primary dielectric and it's the best I've heard in my system.

All the best,
Nonoise
I would say what is the best jacket for WHAT PURPOSE?
Teflon is good for clarity, but not nearly as good for bass as some other types in insulation.

I refer to Kimber using a non Teflon insulation in products touted as have better bass response.
And in my experience, yes they do.
Kimber Hero, KS1116/1016 and Speaker cable VS.