It's been my experience that higher quality flannel doesn't shrink very much. Even the quilters flannel sold at joannes has little shrinkage, about 3-4 inches over 7 yards. The quilt shop stuff was about 2-3 inches over 7 yards, often less. Joannes snuggle flannel shrunk about 7 inches over 7 yards. If you are combining
flannel with regular cotton on a quilt top, I would definitely preshink.