I have a king sized flannel quilt that I made prior to washing the fabric. I love it. All of the fabric is from a quilt shop. It washes beautifully, although it is heavy. When I work with flannel from JoAnn's, I wash it because the quality and thread count varies a lot. I find that flannel is very easy to work with. It doesn't slip or slide. It kind of sticks to the other pieces of flannel. I don't understand your concern about pinning.