Woven mesh is often stronger due to the higher fiber density, but it serves as a poor scaffold for fibrous ingrowth. Permanent or absorbable synthetic mesh is available. Polypropylene, polyester, or expanded polytetrafluoroethylene are the most common permanent materials (ePTFE). Polypropylene has been used in hernia repairs since the 1980s while expanded PTFE (ePTFE) products have become more popular since their introduction in 2001. Mesh can be used alone or in combination with other methods such as staples, screws, and glue for tissue repair. It provides multiple points of contact for healing and can limit pain caused by movement of the injured organ. Mesh is commonly used in hernia surgery and colorectal cancer surgery. Mesh can be classified according to how it is woven or knitted: flat mesh, sheet mesh, tubular mesh. Flat mesh can be made from a single layer of thread that is woven or knit into a fabric. This type of mesh is easy to sew into shape and allows tissue to grow through holes in the mesh. Flat mesh can be made from natural fibers such as cotton or linen or from synthetic fibers such as nylon or polypropylene. Sheet mesh consists of two or more layers of material that have been stapled or glued together. These strips can be flat or curved and can be woven or non-woven.