The standard sidewall covering is called Phylon. The high gloss is called Gel Coat. The difference is that the Phylon has less shine and a bit of a rougher finish. The Gel Coat is a smooth shiney surface. Mostly cosmetic I guess and maybe easier to clean and wax.
We ordered both of our Bighorns with Gel Coat. I like it. I feel that if you are going to have a luxury coach, make it look like one.
Peace
Dave