Acrylic plastic—How is it made?

Starbucks channels


Polymethyl methacrylate is a plastic containing one or more derivatives of acrylic acid.
We know it simply as acrylic.
It is sold under many trade names: Plexiglas, Lucite, Acrylite, Perspex, Acrilex and Crystallite.

There are two types of acrylic sheet commonly used by the sign industry—cast and extruded.


Cast acrylic is made by injecting the ingredients into molds as a molten liquid, about the consistency of syrup, in one of two ways. The “cell cast” or “batch cell” method is made in sheets in a mold made of two plates of polished glass with gaskets at the edges. The liquid plastic fills the cavity between the two plates of glass and may be heated. Several plates may be stacked to produce multiple sheets of acrylic. After curing, the molds are disassembled and cleaned for reuse.

“Continuous cast,” is a higher production method. The molten mixture is cast between two continuous sheets of polished metal in much longer runs as it goes through a series of heaters for curing. Again, gaskets seal the edges.

Cast acrylic is polished and is known for optical clarity. It is harder than extruded acrylic and less prone to scratch. It is also more heat resistant, which is why cast acrylic cuts so much cleaner when machined, whereas extruded acrylic tends to melt behind a saw blade.


Extruded acrylic is a less costly process and provides the larger share of acrylics used in the sign industry. It is manufactured by forcing the semi-molten acrylic mixture through forms and rollers.

Acrylite FF is an example of an extruded acrylic sheet. Acrylite GP is cast.

Airplane and helicopter canopies are made from cast acrylic because of its optical clarity.
Plastic sign faces are mostly extruded acrylics.

Are your ADA-compliant signs really ADA-compliant?

ADA sign picture

If you are involved in the manufacture of interior signs in the United States, you are aware that many of them are required to be compliant with the Americans with Disabilities Act. But if you have not kept yourself informed of the latest ADA Guidelines (ADAAG), your sign work may not be in compliance. This can put your customers at risk.

The latest changes were written in 2010 and were voted into law March 15, 2011. All public-accessible facilities were required to observe these new guidelines by March 15, 2012. The guidelines include some significant changes in the specifications for fonts. Noteworthy is the requirement for tactile signs to use sans serif letter styles in all upper case only. However, even many sans serif styles are not compliant—like Helvetica Medium and Helvetica Bold. Why? The strokes are too heavy. The new guidelines require the thickness of strokes to be no greater than 15 percent of the letter height, based on the height of the capital “I”. That rules out most bold-stroked letters. Helvetica Regular and Helvetica Light are compliant. Helvetica Ultra Compressed qualifies, too.

The width to height ratio is also being spec’d by the new rules. The width, based on a capital “O”, must be between 55 percent and 110 percent of the height, again based on the capital “I”. That means Helvetica Extended is non-compliant, as is Helvetica Compressed. That means, too, that squishing the width of a letter to make it fit a particular size wall sign may render the sign non-compliant (not to mention ugly).

Other changes in the new guidelines include a rule on line spacing. And letter spacing is now mandated (it’s wide). The dimensions of Braille cells are now specified, as is the structure of a Braille dot. And Braille must always be placed directly below the lettering. It cannot be to the side anymore, with one exception: Braille for an elevator button can go to the side.


ADA illustration

There are other changes as well, including changes to the penalties for violations. The penalty for a first violation is now 75,000 dollars.

If a sign maker is not producing ADA-compliant signage where it’s called for, and it results in a non-compliance action against a client, it’s easy to see how the sign company’s survival could be threatened. Think: who would knowingly continue to buy from a sign producer that was responsible for one of its customers being hit with a costly non-compliance proceeding?

Here is a pdf file comparing the 1991 and 2010 standards, and pointing out the changes. Signs are in section 703 of the pdf.

1991 and 2010 ADA Standards

Here is a link to the official published standards:

ADA Standards. Section 703, Signs.

Electric signs and sign goobers

Most sign companies in the US do not have real, live electricians on the payroll. The typical sign shop doesn’t want to pay what a licensed electrician would demand for wages, so lesser paid employees are trained to assemble and wire internally-illuminated signs, and service them after installation. The learning curve is not steep, as electric signs are very simply built. These employees will have varying degrees of electrical knowledge and ability, ranging from people who are very experienced to complete novices. Pre-cut knock-down kits are available that allow practically anyone to put together lighted signs with a minimum of fabrication equipment. They can be assembled with screws, high-bond adhesives or by welding. Translucent vinyl lettering can be used for the plastic faces, eliminating the need for painting. This type of work can be done by the most unskilled labor. It can be done in someone’s garage.
In fact, if the general public in this country knew how inexperienced some people are who work on electric signs, they would be surprised.
In the US, using unskilled workers for this type of electrical work is usually not a problem for licensing authorities. Sign companies in most municipalities are legally allowed to do limited electrical work without a license, without any credentials at all, in fact. Further, after paying the fees and receiving an inspection of a sample completed sign, most any shop may receive UL certification.

So just as practically anyone in this country can start a sign company and be a “sign designer,” practically anyone can make electric signs, too. I’m not saying this is bad, necessarily. But just as I would like to see sign makers strive for better design work and a better understanding of design principles, I would also like to see sign makers improve their knowledge of electricity and their understanding of basic electrical troubleshooting.

Though this site will be primarily devoted to design, there will also be posts related to lighted signs.