Traditionally known as Irish Flax Felt, Roofmaster continues to provide Black Sheathing Felts for those specialized roofing applications. This black sheathing is made from very long jute fibers and bitumen. These unique longer jute fibers exhibit superior tensile strength and conformity to odd shapes. Use as an underlayment with hot asphalt to flash around scuppers, vents, drains, masonry walls, shower pans and all deck flashings. Great for adjoining new and old roof surfaces together. Also known in the marine industry as ship's felt.