REX Synfelt is a high strength woven synthetic roof underlayment that is the most slip-resistant in the industry. Synfelt is 20 times stronger than felt, won't tear off or buckle when wet. 10X lighter per square and 20 times stronger than 30 lb. felt. 10 squares per roll weighing only 28 lb. UV resistant and can be exposed for up to 6 months. Light gray color reduces heat and provides cooler working surface. Pre-printed nailing pattern speeds installation. Made of 100% polypropylene. Class A fire rated with 25 year limited warranty. 48'' x 250' rolls.