Acrylic is a very common plastic used in a variety of applications such as point of purchase displays, window replacements, and anywhere you want the clarity of glass without the safety or breakage concerns. Acrylic is also much lighter than glass and can easily be heat formed into any number of shapes. Although the majority of all acrylic is sold in clear, it is also made in common colors for signs, or tinted solar colors for windows and skylights.
There are two main processes in producing acrylic sheet. It can be extruded or cell cast. The extruded type simply means that a machine is pushing the liquified acrylic monomer between a series of rollers designed to flatten and cool the sheets as they run through the extrusion equipment. This most cost effective form of acrylic manufacturing is probably 80% or more of all the acrylic on the market. The other manufacturing process is a cast acrylic. This form is made by pouring the liquid acrylic monomer between 2 sheets of highly polished glass sealed with a rubber gasket. This cell includes heat activated hardeners, or catalysts, and as the cells are gradually heated, typically through a series of water baths, produce a single sheet of solid acrylic. What you end up with is an acrylic sheet with little to no stress, and by virtue of the manufacturing process, is stronger due to the higher molecular structure of the sheet. This more time consuming and expensive process is used mainly to manufacture thicker sheets or when the material is going to be used in an application where strength is an issue, such as aquariums or aircraft canopies, or when there is going to be some machining done to the acrylic. When you attempt to machine extruded acrylic the heat created from the machining tends to release any stress put in the material as the force of the rollers squeezed the material to make it thinner. You wont have this problem with cast acrylic since there was no stress introduced during the manufacturing process. However, one of the benefits of extruded vs. cast is that tighter thickness tolerences can be achieved during the extrusion process that in the casting process.
Below is a list of common trade names and the way they differentiate between their cast and extruded sheets.
Plexiglas - Plex MCM is extruded
Plex GM is cast Cyro- Acrylite FF is extruded
Acrylite GP is cast Lucite- Lucite CP is extruded
Lucite L is a hybrid of extruded and cast called continuous cast