Velocity Factor in Single Conductor Wire

[Ag6cx]

I am currently trying to find technical or theoretical basis for Velocity factor (Vf) of single conductor bare copper and that of such wire with various insulating materials.

I'd appreciate comments and links.

This site, under the topic, postulates for bare wire, them adds comments re: insulation.
But none of this is s offered with scientific or technical support.

Can you be of assistance?

Reply [email protected].

Thank you