It's not necessary to preshrink fabric that will be used with polyester batting -- as long as you do a "normal" amount of quilting. Quilting binds the fabric layers to the batting so that the batting controls shrinkage. IOW, when quilted, the fabric cannot shrink more than the batting allows. This doesn't work with tied quilts because the fabric is not "one" with the batting; for tied quilts, or for quilts whose quilting lines are far apart, you do need to preshrink the fabric to avoid distortion from fabric shrinkage.