The term “acrylic” is used for products that contain a substance derived from acrylic acid or a related compound. Most often, it is used to describe a clear, glass-like plastic known as poly(methyl) methacrylate (PMMA). PMMA, also called acrylic glass, has properties that make it a better choice for many products that might otherwise be made of glass. There are two basic types: extruded and cast.
Many different products are made from acrylic, including shower doors, bath enclosures, windows, and skylights. It is many times stronger than glass, making it much more impact resistant and therefore safer. Falling against an shower door will not likely break it, for example, and baseballs that crash through glass windows will, in most cases, bounce off acrylic windows. It also insulates better than glass, potentially saving on heating bills.
Acrylic glass is also very clear, allowing 92% of visible light to pass through it. Very thick glass will have a green tint, while acrylic remains clear. It also weathers well, keeping its clarity over the years without turning yellow or breaking down when exposed to sunlight over a long period of time.
Another advantage of acrylic is that it is only half as heavy as glass. This makes this material easier to work with, and makes it a better choice for projects where weight is an issue. It can also be sawed, whereas glass must be scored.
Virtually all major public aquariums now build display tanks out of this thermoplastic, and it is often used in many other buildings. When this material is just over 1 inch thick (about 25 mm), it is bullet resistant; the presidential motorcade, the pope’s booth-vehicle, teller enclosures, and drive-through window enclosures all feature bullet-resistant acrylic. It is used for airplane windows as well.
Misconceptions and Disadvantages
There are some misconceptions about acrylic acid (CAS No. 79-10-7), namely that it yellows, turns brittle, and cracks over time. Though this might be true of cheap forms of plastic, it is not so with acrylic. If taken care of, this material can remain new looking for several decades, regardless of age or exposure to sun. Some people worry that it scratches too easily, but unlike glass, scratches may be buffed out.
For all of its advantages, there are two disadvantages of acrylic: It is more expensive than glass, and if exposed to a direct flame, it will melt and eventually burn. Burning releases toxic fumes, so safety precautions should always be taken when it is being cut with power tools or bent using heat. When it is not cared for properly, or when inferior acrylic is used, it can scratch, and improperly made joints can be very visible.