Polymethyl methacrylate is a transparent thermoplastic often used as a lightweight shatter-resistant alternative to glass.
The reason to use PMMA in 3D Printing is because its transparency, surface quality & mechanical properties are very comparable to Poly Carbonate. But PolyCarbonate is quite hard to work with on machines that don’t have high temp capability, & thats where PMMA comes into play.
We have had good results printing it just like PETG.