Where the number comes from
UL 2218 is an impact-resistance standard. A steel ball is dropped onto the shingle from a fixed height, twice in the same spot, and the shingle is then examined for cracking on the back of the mat. The class is set by the size of the ball it survives: Class 1 is 1.25 inches, and Class 4 — the top — is a two-inch ball dropped from twenty feet.
That is the whole of it. There is no brand, no tier and no membership involved, which is exactly why it is worth knowing: a manufacturer cannot award itself a Class 4, and a roofer cannot upgrade you to one with a sticker.
What it does on a real roof
A Class 4 shingle is built to bruise rather than to fracture. The mat is modified so the stone deforms it instead of splitting it, which is what stops the mat from failing quietly and letting water in months later. It is heavier than a standard architectural shingle and it usually costs more per square.
What it is not is armour. A Class 4 roof struck by baseball-sized hail is still a damaged roof, and the granule loss that ages a roof under Texas ultraviolet happens on every class equally. The claim worth making is narrow and true: in the 1 to 1.75-inch range that most of Central Texas' reported hail sits in, a Class 4 roof is materially more likely to come through intact.
The insurance discount, and why nobody here will quote you one
Most Texas carriers offer a premium credit for an impact-rated roof, and several of them set it by county. The size of it is theirs to decide and yours to ask about — ring your agent before you choose the shingle, not after. Any roofer telling you the number is quoting somebody else's product.
One thing we can be precise about: if a claim is paying for the roof, the carrier owes the scope it approved. Upgrading from a standard shingle to Class 4 is normally a difference you choose to pay, and it goes on the written scope as a line you can see.
When it is not worth it
On a small, sheltered roof under mature trees, on a house you are selling this year, or on a roof where the money would be better spent on ventilation that is currently cooking the shingles from underneath. We would rather tell you that than sell you the upgrade — the decision belongs on the scope, next to the price, where you can weigh it.