To me there is no comparison between the two. Glass- breakable,sharp edges(unless tempered=$$$)and heavier that plexi.
Plexi- lightweight,easy to work with(cut, drill, etc.)
I use a quarter inch thick super scratch resistant on all my cages so scratching isnt a problem and it looks like real glass too- very clear.
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Jaye- " When you try of all your forces to make your own way, you will help some of others and will be helped by others. As long as you do not make your own way, you cannot help anybody, and nobody can help you. " (Shunryu Suzuki)