Originally Posted by Noreastern
In a perfect world it scratch resistant, strong as steel
, affordable and would not "cloud" after years of UV ex-poser.
Back to the real world it seems like everything is a compromise.
Acrylic (Plexiglass) should not cloud, though it may develop crazing which can be lessened by annealing the material after it is cut and drilled. It is prone to scratching and is affected by some cleaners and solvents. Plenty strong and, with proper care, should last the life of the boat.
Polycarbonate (Lexan) will cloud with time. Very impact resistant. Can be had with coatings that will protect from scratching and UV damage.
Tempered glass will not cloud, is very resistant to scratching, will not craze and is impervious to most solvents. Also has a low coefficient of thermal expansion so less prone to leaking over time. It would be my choice for portlight replacement.