I prewash everything. While bleeding colors are an issue, I'm more concerned about shrinkage. I have noticed that all my quilting cottons, with the exception of batiks, shrink along the width of fabric, some as much as 2". I have found this to be true even with name brands. They don't seem to shrink at all along the length. I'm concerned that if I use the fabric without prewashing, my quilt will be distorted because the shrinkage is only in one direction.