I prewash everything except precuts - I have made a quilt with Hoffman Bali pops and didn't prewash and it was fine; it was black fabric all around the batiks so any bleeding would have been hard to see but the color catcher I threw in came out a very pale yellow (from batiks that were brown/black/yellow) so I think that's a pretty good sign there wasn't a lot of dye free in the water.