It used to be that fabrics were washed to remove the formaldehyde from the fabric used in processing it. However, the "finish" used on fabrics, now, are not harmful and do not necessarily need to be washed out. When doing foundation piecing, it is often helpful to have the fabric new and unwashed. Shrinkage is also not an issue if using cotton batting as both the fabric and batting will shrink about 3%. Shout Color Catcher can be used with any fabrics that may fade. It is, ultimately, a matter of personal preference.