Abstract: A roof covering includes a roofing mat formed from fibers of a fiber material. The fibers are coated with a sizing. The roof covering also includes a coating material that coats the mat. The coating material is based on an organic material. The sizing includes a sulfur-containing material that bonds to the fiber material. The sulfur-containing material has sulfur groups that form cross-links with the organic material. In another embodiment, the coating material contains sulfur added to the organic material. The sizing includes a bonding material that bonds to the fiber material and that bonds to the sulfur. The sulfur forms cross-links with the organic material.