My understanding is that the Synthrapol gets rid of the excess dye in hand dyed & batik fabrics. I only pre-wash batiks, hand-dyes & Jinny Beyer fabrics. A quilting teacher told me that Jinny Beyer does not allow the fabric manufacturers to use some sort of chemical that lessens the change of the dyes running. I do not know if that is still true though, but, just in case, I'm more careful with her fabrics.