The Class 4 rating means that a sample of the product did not crack when hit twice in the same place by a 2-inch steel ball, the equivalent of a sizeable hailstone. Consumers should keep this in mind when using the UL standard as a gauge of quality. The IBHS cautions that while some materials may test well, they may perform poorly in practice. For example, some roof coverings may resist cracking, the measurement criteria of the UL 2218 standard, but can be dented and dimple. Homeowners also should be aware of a roofing material's wind and fire resistance features as well.
Good advice is available from design professionals, insurance companies and roofing installers.
A list of roof coverings that have met the UL 2218 standard and achieved a Class 4 rating is attached.