Take it from someone who knows, WASH flannel first. On one of my quilts, I did not wash it until after it was quilted, and it came out all wonky, due to the additional shrinkage. It would make you feel (and look) bad if that happened after you gave the quilt away. Also, some flannel is very thin, and doesn't hold up well to washing. You would want to know that, too, before you put it on a quilt.