Textile and industrial fibers respond to the environment according to their chemical composition and microstructure. Since fibers are typically semi-crystalline, they are generally more stable to both chemical attack and temperature then are wholly amorphous linear polymers. Polymer fibers are very good; indeed, they are the material of choice in some applications, yet they perform poorly in other environment. For example, polyolefins are virtually inert to inorganic, making polyolefin fibers useful as battery separator; however, polyolefins, like most other polymers, do not resist degradation in ultraviolet light. Consequently, polyolefin tent fabric is stabilized so that it can tolerate long exposures to sunlight. We will probe into the cause of poor ultraviolet stability in polymers and discuss ways to stabilize fibers.