HelpfulGardener.com

I now glass is very expensive for a greenhouse but the light comes through so well can anything beat it? It does out last other materials! The double glass window is insulated but should a plastic third cover be added?

Years ago I had a very small greenhouse with fiberglass...it clouded up in a couple years.
The greenhouse I have now is double-wall polycarbonate. So far so good after 3 1/2 years, but on one thread some people had trouble with this.
Plenty of light comes through, plants grew great.

I had a glass green house. Now I have a Double Wall Poly Carbonate green house. I prefer the Poly Carbonate because it holds the heat better than the glass one did.
The Cons are, the double wall polycarbonate panels are more expensive than glass, and the wind has blown panels out a couple of times.

Double wall poly actually has better insulating properties than double glass, is much lighter, cheaper, and does a better job of diffusing the sunlight so you don't burn your plants.