I've been noticing a lot of 80's and early 90's corvette convertible tops with the clear rear plastic windows turning white and some turning yellow exactly like the polydome does so I did a little research and found out that the corvette rear windows are made of polyvinyl. I always thought that maybe the polydome was made out of vinyl. After seeing those older corvette windows I bet the polydome is made out of the same thing, polyvinyl, it would make sense as it is called polydome. The next time you see an older non taken care of classic corvette with the plastic window in it's top take note of how much it looks like the ailing polydome. And they make restore kits for those clear windows that is supposed to get the window clear again and make the polyvinyl soft and pliable, maybe those kits could be used on the polydome, just a thought.