Unidirectional (all fibers are parallel). In a 0-degree orientation, aligned with the fibers, unidirectional (UD) carbon fiber provides high bending strength against the progression of forces, which makes it perfect for the carbon-fiber prosthetic blades used by Paralympic sprinters. In a 90-degree orientation, perpendicular to the fibers, it flexes. In either orientation, it has low torsional strength. In all applications, another layer of fabric, such as Perlon, must be laid under and over UD carbon-fiber weave.