Is there an invisible, solid material with the refractive index of air?

[Archosaur]

I think it would be swell to have a sphere made of a clear, solid material that had the refractive index of air, because it would essentially be invisible. Is there anything even close to this?

 

[Xerxes1986]

The closest I think you are going to get is Aerogel, which can have a index of refraction as low as 1.1 (air is ~1).

 

[Archosaur]

It's not quite clear, but that almost makes it cooler. Good thinking!