GAF Deck-Armor Premium Breathable Underlayment provides a critical layer of protection under your shingles against wind-driven rain and other sources of moisture. Its unique breathable technology allows moisture to escape the roof system, helping to prevent premature roof system deterioration. Made of tough synthetic materials, it resists tearing and helps ensure long-lasting protection. Each roll of Deck-Armor covers approximately 1,000 sq. ft., which results in less rolls to carry and install versus typical asphalt felts.