Retayne and Synthrapol do different things. Synthrapol washes out and captures excess dye and keeps it from depositing back on the fabric. Retayne helps to better "set" dye to the faric. I hand dye and use both: Syntrapol to get rid of the extra dye and Retayne to keep what did set on the fabric "attached" better. Batiks sometimes have extra dye that hasn't been fully washed out so Synthrapol might be better, but it won't "set" dye that has trouble attaching itself.