Plexiglass is not real glass; it is a type of plastic substitute. The name “Plexiglass” is a registered trade name for polymethyl methacrylate (PMMA), a synthetic polymer. This material is fundamentally different from the inorganic composition of traditional glass. Confusion often arises because PMMA offers the transparency and clarity associated with glass.
The Chemical Identity of Plexiglass
Plexiglass is derived from petroleum products and is classified as a thermoplastic. Its chemical structure is based on long, repeating chains of molecules called polymers. Specifically, it is poly(methyl methacrylate), created through polymerization where individual monomer units link together. This chain-like structure allows the material to be melted, molded, and reformed when heated. The defining characteristic is its organic, carbon-based molecular backbone, which is the hallmark of all plastics.
Defining Traditional Glass
Traditional glass, typically soda-lime glass, is an inorganic material composed mainly of silica (silicon dioxide) derived from sand. Silica makes up about 70–75% of the total composition. Other primary components are soda (sodium oxide) and lime (calcium oxide), added to lower the melting temperature and act as a stabilizer. Glass is created by heating these raw materials to about 1500°C until they melt into a liquid. The liquid is then cooled quickly to prevent the atoms from arranging into a crystalline structure. This results in an amorphous solid state, a key structural difference from the highly organized, chain-like structure of a polymer.
How Their Physical Properties Compare
The distinct chemical structures of Plexiglass and glass lead to significant differences in their physical properties. Plexiglass is lighter than glass, weighing approximately half as much for the same size and thickness. This low density is a direct result of its polymer composition.
Plexiglass is far more resilient than traditional glass, often cited as ten times more resistant to shattering. When a polymer breaks, it tends to crack or fracture into pieces with duller edges, unlike brittle glass, which shatters into sharp fragments. The high optical clarity of PMMA is notable, transmitting up to 92% of visible light, slightly more than the 90% transmission rate of conventional glass.
As a thermoplastic, Plexiglass is highly flexible and easy to fabricate; it can be cut, drilled, and molded at lower temperatures using standard tools. Glass requires specialized tools and high heat for shaping. However, this thermoplastic nature means Plexiglass is flammable and will ignite when exposed to fire, whereas glass is non-flammable and highly resistant to heat.