Roofing materials are given a rating (Class 1, 2, 3, or 4) based on the level of impact they can handle without cracking. Class 4 is the highest possible rating. It’s measured by dropping a 2-inch diameter steel ball at a height of 20 feet directly onto the roofing material. If the shingle’s mat does not crack, it receives a Class 4 impact rating. Class 3 is measured by dropping a 1¾-inch steel ball from a height of 20 feet.