This is a function of the permittivity of the material. A Vacuum is 1, the lowest possible. Air is 1.0006 so you won't see much difference. Fiber optics of v

This is a function of the permittivity of the material. A Vacuum is 1, the lowest possible. Air is 1.0006 so you won't see much difference. Fiber optics of various types are usually on the order of 2 to 3 (closer to 2).