I have starched flannel heavily before cutting (for a pieced quilt). I had also prewashed it so let it shrink (about the only fabric I ever prewash for shrinkage). Heavy starching made it much easier to cut and piece the pattern accurately. It stopped the flannel from stretching while I worked with it. All of the starch washes out with the first washing, so the flannel returns to its original softness. My starch was a 1:1 solution of Sta-Flo liquid laundry starch and water, "painted" onto the yardage with a large wall painting brush. Tossed in the dryer, then ironed with steam.