RoofGard-Cool Grey is an advanced three layer structure; a woven polypropylene core (durable and high strength) which is polyolefin coated on both outer layers. This is a superior synthetic, light weight, non-breather underlayment. The material comes printed with installation lines at approximately 1" spacing to assist in shingle application alignment (chalk lines are still recommended for accurate alignment). The UV stabilizer in all layers of the material means it may be used as a temporary covering for up to 3 months. RoofGard- Cool Grey is an impervious, high tear strength underlayment ideal for secondary water shedding beneath shingled roofs. It is incredibly flexible, and therefore easily installed around vent stacks, dormers, chimneys and other roof-top structures.