A high-performance, engineered material, typically made from woven or spun-bonded polymers like polypropylene or polyethylene. It is installed over the roof deck and beneath the primary roofing material (shingles, metal, tile) to serve as a high-tech secondary water-shedding barrier.
Unlike traditional asphalt-saturated felt, modern synthetic underlayment is water-repellent, meaning it does not absorb moisture. It is exceptionally lightweight yet offers superior tear strength, durability, and UV resistance. Many variations also include specialized features like non-slip walking surfaces for installer safety, full self-adhesion for high-performance water sealing (often called “ice and water shield“), or micro-perforations to allow trapped vapor to escape.
