Wow great info...I was just thinking about how I could make a sunvisor and like magic we have one...
Did you consider using a tinted plexiglass? I'm thinking strictly as a sun visor and a clear one wouldn't be much good. I might take it one step farther and make it a bifold with the top several inches black and tinted under it so you can see through it...like car visors...you can't see through the visor but when you add the slightly tinted one to it ...it's just better.
Mine is a kind of gray, I'll gonna buy a tinted one soon, it is not so expensive. I'm also buying one made out of LEXAN "shatter proofed.