I wash my flannels sometimes.....if I am making a new quilt from quilt shop quality flannel (12-14 dollars a yard usually), I usually do not wash if the flannel is all from the same manufacturer...if I am making a quilt and the flannel is from a lot of manufacturers, I usually do wash everything before, unless I am making a rag time quilt, I do not....If I purchase a cheaper quality backing I most always wash it, as cheaper flannel usually shrinks quit a bit.....