I always prewash. A pain, but I must. Now I put it in the washing machine with a tiny bit of detergent, and agitate it by hand. Then spin. Then fill with water--agitate by hand again, spin and dry. An extra step, but I never wash the quilts after I make them, except for ragged flannels, and even those I might spray with water and dry. I like the unwashed look for as long as it lasts.