Is there any hit on performance with 2 sided materials vs non 2 sided?

Austin casts Necro, it isn’t very effective…

Could we all get some more detailed information on this? Is the material shader cost doubled with 2 sided? How does the culling work, would BMAliens example render the full sphere? Does it then need to draw the inside as well? Is that more geometry being added to the scene?

Are there tips and/or tricks to combating the necessity of a 2 sided material?

Thanks!