Plexi (polymetylmetakrylat) is an acrylic plastic but it cracks more easily compared to Lexan (polycarbonat).

Also I think Plexi is more sensetive to solvents (alcohol for an example).

Therefore, I really would recommend using Polycarbonat, the drawback is that it's hard to find in any colors, the most common is clear transparant and smoke-colored.

One of the best parts with Polycarbonat is that it's viritually impossible to crack when pinning!!
Best regards

Clas