A Class 2 impact shingle is one that has been assigned a Class 2 rating by Underwriters Laboratory, or UL. Testing performed by UL determines the degree of stress that newly manufactured shingles can endure. Steel balls, measuring from 1.25 inches to 2 inches in diameter are plummeted against the shingles at a speed of 90 miles per hour. A shingle is assigned a Class 2 rating if it does not rupture or crack when hit by 1.25-inch balls dropped from 20 feet above.

The highest rating is Class 4. These shingles withstood 2-inch balls under the same testing conditions. A Class 1 rating means the shingles withstood 1.25-inch balls, and a Class 3 rating means the shingles withstood 1.75-inch balls. The impact rating is important to know. For example, if you live in an area where winds are gusty and hail is common, you would want shingles with a higher impact rating, such as a Class 3 or Class 4. However, if you live in a mild climate where windy conditions and hail are not as big of a threat, Class 2 shingles will suffice.