I wash all my quilts once I complete them. I do not prewash my fabrics. Washing takes the dirt and oils out that may have gone on the quilt during construction. Washing also takes out any dyes or other chemicals in the fabric/batting placed there by the mfg. Washing/drying allows the fabric/batting to shrink and set together. I always throw a Shout Color Catcher in the wash to collect any color released during washing.