Indigo and Polyester

Q: Can I dye polyester fabric using natural indigo dye?

A: Natural indigo vats do not effectively dye polyester.  It seems the indigo pigment molecule doesn’t have a way to properly bond to polyesters.  I’ve gotten blue-greys dyeing polyester in the past but they don’t look great and are never that saturated and tend to wash and sun fade very easily.  Natural indigo works best on natural fibers from plants or animals.  You will even notice that if you dye a garment that is made of natural fibers (say, cotton) but is stitched using polyester thread, the fabric will dye but the thread will stay more or less white.