I only prewash fabric that is from discount stores, and that fabric I wash with hot water so it will do all the shrinking it is going to do. I have had some bad experiences with some of the lower price fabrics not shrinking uniformly and bleeding after 2 or 3 washes. It does not seem to do that after the hot water. I also use the color catchers. When I am using fabric from the fabric store and I am worried about it bleeding I cut a piece off and wet it then leave it wrapped in some white muslin overnight to see if it bleeds. If the expensive fabric bleeds I take it back to the store I bought it from!!!!