There are two kinds of vinyl, cast and calendared. The calendared is made by squeezing a blob of hot vinyl through some rollers into a thin (3-4mil) sheet. It's cheap to do, but the vinyl wants to shrink back a bit after a couple years because it was forced into a sheet without being all the way melted.

When the cast vinyl is made it is completely liquid and pours in a very thin (2mil) sheet from a pool of molten vinyl. As it cools (casts) in its sheet shape, it has no stress and will maintain its dimensional integrity for much longer. This material costs about 3 times the money to manufacture, and being thinner it is a little harder to apply, but it is the only way to go if you want it to last. (And to survive the car wash).

All our kits are premium 2mil cast vinyl with an expected outdoor life of 7 yrs.  Anything requiring print, which is to say anything not of one solid color, is coated with clear cast film to protect the print from abrasion and to filter ultraviolet.These printed kits are therefore shinier than kits without print.

You will find no better quality on the web.  You will, by contrast, find plenty of people who will sell 3.5 mil gloss intermediate and not bother to mention it.  It is very shiny, stretchy, and nearly impossible for a consumer to detect until it fails early, so be wary. To be fair, intermediate vinyl does fine for a couple years, so just be sure you get what you pay for.