As you look at that old paisley jacket in disgust, you wonder: how does bleach affect polyester? Unfortunately, bleach is not the best bet for getting rid of undesirable colors or patterns in polyester fabrics. In fact, bleach only works successfully with natural fabrics such as cotton, rayon or linen, while bleach affects polyester in such a way that cannot be undone or repaired. In some ways—such as coloration—bleach does not affect polyester much at all.
For starters, if you are attempting to bring your polyester to a bright-white hue, this will not be the end result. Because polyester is a synthetic fabric, it is basically colorfast. Any dyeing with synthetic fibers is unreliable, and you will likely be stuck with an unattractive yellowish color if bleached.
Another reason to avoid bleaching polyester is that the once-strong fibers will become very damaged and brittle. This makes for a pretty uncomfortable piece of clothing. Synthetic fibers are also heat-sensitive and may shrink, melt or burn in high temperatures. This could involve such an innocent act as washing or drying the polyester material in a hot machine or exposing the fabric to excessive sunlight after bleaching.
While bleach is not a good match for polyester, don't be discouraged. If you absolutely must whiten polyester, the best alternative to bleach is a good fabric paint. And with textile paints, don't be stingy: the better the quality, the less it will affect the feel of the fabric. Now that you know, go ahead and paint the heck out of those ugly old polyester prints, but leave the bleaching to the natural fibers.