Variables affecting the light and weather resistance of fibers, and methods for determining the relative durability of fibers, are discussed. Comparative data on the strength retained by various fibers after outdoor exposure in Florida for periods ranging form 1 to 36 months are presented. The effects of different exposure conditions and fiber characteristics on the outdoor durability of the test items for direct and under glass exposures are illustrated. Exposure data for 50 different, commercially-available yarns representing 14 different generic class of fibers are reported. This test was concluded for DuPont by Georgia Institute Technology.