I have made at least 6 flannel quilts and never have washed flannel before quilting. I washed after the quilt was done and it shrinks like cotton fabric and gives it the old look. Maybe if a person buys real cheap flannel but I buy the flannel at the quilt shops. I have bought flannel from JoAnns and that shrunk more but it didn't affect the quilt. I have used flannel for backing on a cotton quilt and have had no problems.