I would think that Lexan or some other brand of polycarbonate sheet would be best. It is important that it be strong enough to support a person who falls against it, etc.
A 4' X 8' X 1/4" polycarbonate sheet is around $270 and comes in many shades as well as clear.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida