Similarly, copper is faster than glass too (but not faster than air). The trade folks refer to copper in terms of "velocity factor". Example, some arbitrary RG-

Similarly, copper is faster than glass too (but not faster than air). The trade folks refer to copper in terms of "velocity factor". Example, some arbitrary RG-6 I'm looking at has a velocity factor of 81%. Equivalent refractive index is 1/.81 for ~ 1.23.