Acrylic. Full name polymethyl methacrylate. Plexiglas is a trade name of one, not sure who makes the stuff in our canopies.
 
Mhmm.. interesting... I was searching for an aftermarket windshield for my motorcycle (BMW K1200LT) and I found this video comparing acrylic to polycarbonate.

I think that a polycarbonate canopy for RV would be a great safety enhancement... if it can resist to a shotgun, it can probably resist to a flip over. Unfortunately, I don't think that it exists.
 
There is one more reason that speak against Polycarbonate: it doesn't like fuel. PMMA (aka Plexiglas) is fuel resistant.:)