Product characteristics Apy can prevent yellowing after treatment, especially for light color, bright color or white fiber. Nylon fibers are often yellowing due to the following reasons: (1) Yellowing caused by the influence of NOx or Sox gas in the air. (2) Yellowing caused by exposure to sunlight. (3) Yellowing caused by antioxidants (e.g. BHT) contained in films for packaging materials. (4) Yellowing caused by the influence of lignin contained in handling cartons such as corrugated paper. The yellowing caused by the above is generally not just a single cause, but mostly caused by many factors. In particular, the bright color system or white system is more seriously affected. Therefore, the most important development of apy is the products developed for the above yellowing caused by NOx and Sox in the air and chemicals contained in packaging materials.