Plastic Whitener Chemicals Optical Britghtener for Fibers and Plastics. In Polyster fiber optical Brightener imparts a Pleasing "Whiter-than White" appearance and gives more intensity to some colours as well. Optical Brightener is a Permanent brightener since it is dissolved in the fiber during polymer manufacturing . This Product gives much better retention of brightness over long time versus other methods such as bleaching or surface treatment with topical brightness.