Thanks Fairlane. Any chance I could talk you into linking in your source? I like to read technical stuff and have an enquiring mind. 
@"the same mountainbike"
Sorry I didnāt put in the links in the first place. It was late and I was lazy. Thank goodness for browser history.
For the material, the source is http://calcoast-itl.com/assets/Plastic%20Material%20In%20Automotive%20Lenses.pdf
They mention both polycarbonate and PMMA, which are both widely used polymers. They also give references to the UV and hardening coating.
For the solvent resistance, I used this source: http://www.plasticsintl.com/plastics_chemical_resistence_chart.html
It has tons of info, but you can zero in on one solvent, which makes it easier to read.
The choice of which plastic material to use for a specific application is incredibly complicated. I canāt say I have a grasp on all of it, but have talked to people who do the work, and itās a fun challenge.
I hope thatās a good start.
I used a Sylvania kit on a friends badly fogged headlights.
Contains everything needed, including masking tape and a paint-on UV coating.
It did an excellent job and is still clear after 2 years of being outside (near the ocean [Salisbury MD] if that matters).
āā¦(near the ocean if that matters).ā
It sure does matter. I want my car headlights to be near the ocean, on my car with me in it, 1500 miles south of here! I just battled April storm #2. #1 brought 10" and #2 brought 6" more. #3 starts today and goes through tomorrow! Yesterday morning it was -10F, unbelievable.
Get me out of this place!
@circuitsmith
Thatās good info on the Sylvania kit and your experience.
CSA
Rain or snow? Iād like to get one more use out of my snow blower this year.
@Bing
"Rain or snow? Iād like to get one more use out of my snow blower this year."
Are you serious about wanting to use your snow blower? Itās snow! Iām sick of using mine.
About a week ago I drove past the golf course and it was looking good. I thought this would be a rare year that Itād be open April 1st. Now the ground is covered with a foot+ of snow and more coming. The mail canāt even get through.
CSA
Well you heard the saying when handed a lemon, make lemonade, so maybe a snow man or a whole family of them. Sorry though for the bad weather. Just a little cold here.
Outstanding, Fairlane! Thatās the kind of information I like. Thanks again.
I have used the Gator brand kit I bought at Lowes. It came out nice and so far so good. It did take about an hour to do two lenses from start to finish. It is very important to keep the lens wet when polishing with the drill.
I found the TurleWax kit only lasted about a year. But even after that year the lights just need a quick clean up with what they call clarifying compound or something like that. Luckily there is enough left of to last me a few more years. But I have found the kit works great on plastic watch crystals.
Before:
After:
Toothpaste works pretty well also
Yeah so does Meguireās Plastix. Polishes plastic to like new or better and one $10 container is almost a lifetime supply.
āā¦ almost a lifetime supply.ā
How long is that? 
That reminds me, whenever somebody asks me, "Have you lived here all your life?"
My response is, āNot yet!ā :neutral:
CSA
Iāve heard that, although I havenāt tried it.
Truth is that any micron-sized abrasive in a good suspension media should work well if used with common sense.
For all of those who say it is sun exposure that destroys the lens; My Camry lights are faded/pitted on the vertical portion but the top horizontal portion that gets more sun exposure is still clear. So what gives?
Was there a specific reason car makers went away from glass headlights other than the cost difference? Iāve always wondered thatā¦ Foggy headlights are annoying.
Iāve never had long term luck with cleaning headlamp lenses. They look good for a while, but then quickly degrade again.
Now Iām sold on just buying new headlamp assemblies. I originally wasnāt until I saw what Rockauto was selling them for.
@John Andrew McCormick
"Was there a specific reason car makers went away from glass headlights other than the cost difference? Iāve always wondered thatā¦"
Hereās what I think about it.
Cars are no longer boxy in shape and design, but have become streamlined with better aerodynamics for better efficiency. Therefore headlights also needed to become more streamlined and styled to match the aerodynamic shapes of the car bodies. They have become part of the bodyās shape.
This caused the headlights to get larger and would be more difficult to make and too heavy to utilize glass rather than plastic. Aero headlights made of plastic fit the requirements. Also, larger headlights create a bigger target for stones, so tough plastic makes more sense. Some of these newer headlights are much more difficult to replace than the old glass sealed beams and the resilient plastic keeps that procedure to a minimum.
Back in the sealed beam era I would have to replace headlights due to stone holes which instantly blow the filament. Iāve not replaced a plastic one due to chips.
Now, if the experts could just develop an affordable plastic material that wouldnāt degradeā¦
CSA
Styling. Period. As soon as plastics technology reached the stage where it was possible, the manufacturers got the new headlights approved by the D.O.T. and started streamlining the styling. Since that time, the technology has improved to where the headlight lenses and the directional lenses can be molded into one piece, along with anything else desired, and everything got molded into one. Now itās moving toward multiple LED lamps, and thatās going to change the industry again. Hereās an example.
I've never had long term luck with cleaning headlamp lenses. They look good for a while, but then quickly degrade again.
Thatās because simply polishing them does not replace the protective coating applied by the manufacturer. The uncoated polycarbonate will degrade rapidly from UV exposure (both sunlight AND many headlamps, especially HID) without it.
I recall this being discussed the last time this issue came upā¦