It's any of several approved coatings on any of several approved polycarbonate materials. Coatings are approved for use on particular materials; one can't just select any approved polycarbonate and coat it with any approved coating. This list of approvals is maintained by
AMECA. This system kind of breaks the firmly-held party line that North America doesn't have type approval. Fact is, you have to submit your material and coating to this agency and without their approval it's not legal to use, so if that's not type-approval, what is it? The US (SAE) tests for plastic materials take between 3 and 6
years because the test chips have to be left outside in Florida and in Arizona for 3 years, after which they're allowed no more than 30%(!) haze. That is a slow test with a lax "pass" bar, if you ask me. The rest of world (ECE) test is much faster; it involves the use of an electric arc lamp without a UV shield to rapidly age the material, so the test takes days instead of years. The "pass" bar isn't necessarily strict enough on that test, but at least it allows the latest up-to-date materials and coatings on the market. With the US test, the newest materials allowed on the market are at least 3 years behind the state of the art.
The coatings themselves incorporate physical protection against abrasion and optical protection against UV degradation. They're usually an engineered polymer applied under clean-room conditions and then cured (crosslinked) by UV or heat. Definitely not something that can be sprayed, brushed, or rubbed on in the driveway, garage, or paint booth.
Of course, the aftermarket headlamp manufacturers don't feel any qualm about bogus DOT and SAE or E-markings on their products, so they certainly don't care about compliant materials. Whatever clear plastic they can get the cheapest that won't immediately melt is what gets used.