Sorry to break the bad news here, But being in the plastics business since 1982 polycarb and acrylic are both about the same price for comparable grades. While acrylic sheet in general is less expensive if you request a premium grade the price per pound is same.
PC (polycarbonate) is softer and will absorb moisture in a obvious way by fogging. Hence the alcohol working to defog. It is possible to polish, (gradually scratching surface with finer compounds) however it is not easy.
PC was invented by a chemist at GE in the early 50's Acrylic has been around commercially since the late 30's. Wikipedia has good data on both plastics.
Acrylic will absorb moisture but not show it like PC will. You can polish and re-polish good acrylic over and over again.
as Ron says it can craze, stress or micro crack how ever premium acrylic will be far less prone to it. A good quality Acrylic shield will out cosmetically last PC out side twice as long.
The F15 fighter jet as well as others use acrylic for the windshield due to optics. On the F15 it has to withstand a 600MPH frozen chicken dead on and not break. They were originally machined from solid now are injection molded. That is one heck of a injection molding machine. Was a big deal in our industry in the late 80's or early 90's
All types of plastic will PC, acrylic, etc.. Will deteriorate over time. The lower the grade of plastic the worse it will look over time. It depends greatly upon the additives used such as UV inhibitors & impact modifiers etc...
PC is used in laminated glass for bullet proof glass.
PC comes with a BMW due to European laws like our DOT laws except they have more stringent and enforced laws.
Acrylic can shatter like in the Z Technic videos, It is a well staged demo & they are using really low quality thinner than CEE Baileys acrylic wind shields versus the PC shields they sell. I saw the demo personally at the BMW MOA rally in 2007. However Lets think about reality here. How many people have had catastrophic MOTORCYCLE windshield failure due to incoming objects? If something comes in that large the windshield is the least of your concern.
I use a Cee Baileys and like it much better than OEM. It is very solid and a solid 1/4 thick. It is also clearer than OEM.
For what is worth on my old OEM PC shield Mr. Moto aerosol polish after a thorough cleaning with windex worked really well to clean up. I did this till my new Cee Baileys came in. The liquid Mr Moto polish does not work any where as well at the aerosol.
Sorry for the egg head write up here but felt the need to clear the air on PC versus acrylic.
Originally Posted by RonKMiller
The BMW OEM windshield is made from polycarbonate with a silicone outside layer.
Not "multiple layers".
other current options for the LT (with the exception of V-Stream)
are made from acrylic - a very poor choice as it shatters easily from impact into large dagger like shards. Acrylic windshields are also very prone to "crazing" and stress fractures.
Bottom line: There are no Federal Motor Vehicle Safety Standards for motorcycle windshields.
why 90% of the after market manufacturers use acrylic. MUCH cheaper since it is a commodity plastic, relatively easy to form. Cleans up nicely with polish - about the only good thing I can think of to say about acrylic.
Just like polyurethane foam and vinyl : a commodity "off the shelf" plastic that is absolute JUNK.