Plexiglass is a type of clear acrylic sheet. The scientific name is poly(methyl methacrylate), sometimes abbreviated as PMMA and classified as a transparent thermoplastic. Since plexiglass is a plastic, it is a petroleum-based product. Glass is a amorphous (non-crystalline) solid, an inorganic compound that has cooled from a liquid to a solid without passing through a crystalline state. Glass is brittle, transparent and composed primarily of silicas.
Glass surfaces reflect light more readily than plexiglass surfaces, and this can create unwanted glare or reflections. Many aquarium makers use plexiglass not only for its greater relative strength but also because it offers less glare and increased clarity.