wiki:PCB_Technology

Dielectric Properties

 Dielectric Constant of the permittivity of the material to the permittivity of vacuum, and is denoted as 'Er. For FR-4 (standard PCB material) Er is about 4.5.

'Dissipation Factor  1  2 is the parasitic power loss (as heat) in the dielectric.

 Article impedance formulas.

Materials/Vendors?

PCB Design] tech note from Lattice