Polycarbonate is very strong and ideal where children are about playing or if you have problems with vandals breaking glass!
Is the thread about polycarbonate greenhouses or something different?
The only other rigid plastic I can think of is perspex which is brittle and as far as I know NOT ultra violet inhibited! After a season in daylight it wil go very, very brittle!
Polycarbonate can be single thickness or multi layered with air gaps inbetween giving better insulation. The downside is that the multi-layered stuff lets in less light than the single thickness!