Definitions for "Perspex"
Brand-name. Cast acrylic sold in sheets. Similar to Lucite.
An optically clear, thermoplastic resin, polymethyl methacrylate, used as a substitute for glass in certain applications-such as some picture frames. Perspex is a brand name; a similar product has the brand name Plexiglas.
a transparent thermoplastic acrylic resin
Keywords:  plexi, hence, glass, pretty, difficult
Similar to glass but plastic and pretty difficult to break, hence used on larger pictures.