GAF Shingle Mate 36 in x 144 ft 400 sq ft Felt Roof Underlayment Stair Accessories cutting depth: 1 314835204 cutting depth: 1 A recurring positive is durability over years of professional use Helps prevent wind driven rain (or water from other sources) from infiltrating under your shingles and causing damage to your roof structure or the inside of your home Looks better: fiberglass reinforcement helps resist wrinkling buckling and lies flat under shingles Eliminates the need to slit bubbled felt (which can compromise the waterproof integrity of your roofing system) Lighter and easier to handle than #30 felt Feet) 400 Weight (lbs