Plexiglass vs Acrylic: Is There a Difference?

Plexiglass, Plexiglas, acrylic, PMMA, Perspex, Lucite, ACRYLITE, OPTIX. What the names mean, who owns them, and the one distinction that actually matters when you buy.

No. Plexiglass is acrylic. "Plexiglass" is what most Americans call the material, "acrylic" is what the plastics industry calls it, and "PMMA" is what chemists call it. They are the same clear thermoplastic, polymethyl methacrylate, and any sheet sold under any of those names will have the same basic properties: about 92 percent light transmission, half the weight of glass, roughly 17 times the impact resistance of plate glass, inherent UV stability, and a soft surface that scratches and can be polished.

What does differ is the spelling, the trademark, and, much more importantly, whether the sheet was cast or extruded. That last one is the difference worth paying attention to.

Where the names came from

PMMA was developed almost simultaneously in three countries in the early 1930s, and each company trademarked its own name.

Plexiglas (one S) was registered by Otto Röhm's company in Germany on August 9, 1933. It became the generic word for the material in much of the world, and in American English it picked up a second S along the way.
Perspex came from Imperial Chemical Industries in Britain, where Rowland Hill and John Crawford developed acrylic sheet at about the same time. It is still the everyday word in the UK and Australia.
Lucite was DuPont's American brand, dating to 1931, and became the name for acrylic in jewelry, furniture, and design.

All three are trade names for the same polymer. Eighty years of use turned Plexiglas into "plexiglass," a common noun, the way Kleenex became tissue.

Who owns the names now

This is where it gets confusing, and it matters if you are trying to buy a specific brand.

Röhm GmbH, the German company descended from the original inventor, still owns the PLEXIGLAS trademark in Europe, Asia, Africa, and Australia. In the Americas it cannot use that name, so the same Röhm product is sold here as ACRYLITE. If you buy ACRYLITE in the United States, you are buying what the rest of the world calls Plexiglas.

Plexiglas in the Americas is owned by Trinseo, which acquired the North American PMMA business that had passed through Rohm and Haas, Atofina, Arkema, and Altuglas over the decades. Trinseo's Plexiglas G is the cast grade and Plexiglas MC the extruded grade you will see at suppliers like ePlastics.

Lucite and Perspex are now brands under Mitsubishi Chemical's Lucite International group.

OPTIX is Plaskolite's brand, the house-brand acrylic at Home Depot and other retailers. Chemcast and Spartech are other North American cast-sheet makers you will see at TAP Plastics.

None of this changes what is in the sheet. A 1/4-inch clear cast sheet from Röhm, Trinseo, Plaskolite, or Chemcast will perform the same on a window. The brand tells you who to call about a warranty, and it tells you whether the seller knows what they are selling.

The distinction that actually matters: cast versus extruded

If you take one thing from this article, take this. Acrylic sheet is made two ways, and "plexiglass" can mean either.

Extruded sheet is made by pushing molten PMMA through a die and rolling it flat. It is cheaper, holds thickness tolerance closely, thermoforms easily, and comes in thinner gauges. It is a little softer, chips more on the saw, cracks more readily on oblique cuts and at drilled holes, and has slightly lower optical clarity. It is what the big-box store sells and what most replacement windows are made from, and for a flat pane in a frame it is fine.

Cast sheet is made by pouring liquid monomer between glass plates and curing it. It costs about 20 percent more, has better clarity and chemical resistance, machines and laser-cuts cleanly, polishes better, and comes in thicknesses extruded cannot reach. It is what you want for anything you will cut into shapes, cement, polish, bend, leave in full sun for decades, or look through at thickness.

When a supplier says "plexiglass" without saying which, assume extruded. When you care, ask. Our suppliers roundup covers who stocks what.

What "plexiglass" is not

Polycarbonate (Lexan, Makrolon) is a different plastic. It is far tougher, more flexible, yellows in sun without a coating, and cannot be polished. People sometimes call it plexiglass. It is not, and the two should not be confused when buying a window. Our acrylic vs polycarbonate guide covers the differences.

PETG is a third clear sheet, used for displays and vacuum forming. Also not acrylic.

"Acrylic glass" is a translation of the German Acrylglas and means the same thing as acrylic sheet. "Safety glass" is not acrylic; it means tempered or laminated glass.

Spelling, for the record