Im not sure but I know this...they can be buffed to give them just a little shine if you want. I know that because I recently had a guy polish the exterior, and I specifically told him not to touch the vinyl.
But, I had a couple small scuff marks in them and he swore he could buff them out. I told him to first experiment on the one that was least visible, and he got them both out with light buffing, though it did leave the area just slightly more shiny. He says it would look better if he did the whole thing, but I like the flat flat look.
Not sure what he used though.