trademark name of polymethyl methacrylate, a synthetic organic compound of high molecular weight made by combination of many simple molecules of the ester methyl methacrylate (monomer) into long chains (polymer); this process (polymerization) may be effected by light or heat, although chemical catalysts are usually employed in manufacture of the commercial product.

The material has high dimensional stability and good resistance to weathering and to shock; it is colourless and highly transparent, but can be tinted or rendered opaque by the addition of other substances. It is usually fabricated by molding into solid articles or casting into sheets. An object made of polymethyl methacrylate displays the unusual property of keeping a beam of light reflected within its surfaces and thus carrying the beam around bends and corners of a pipe, bundle of threads, or sheet and reflecting it out through the ends or edges. It is widely used in aircraft canopies and windows, boat windshields, and the like, and for making ornaments, medallions, and lenses for cameras and automobile stoplights and taillights. It is also used in medicine in devices for illuminating and visually inspecting interior organs.