Roof felt | felt shingles | roofing - b&q, 4mm this is bituminous waterproofing systems are designed to protect residential and commercial buildings. bitumen (asphalt or coal-tar pitch) is a mixed substance made up of organic liquids that are highly sticky, viscous, and waterproof.[1] these systems are sometimes used to construct roofs, in the form of roofing felt or roll roofing products.felt, felts