Well most will pre-wash, but while talking to my LQS who longarms also, she looked at me one day and said, why do you want to pre-wash the flannel. ummmm cause it will shrink, I usually use it for backing. She says well my dear think about this for a moment...."Once it is quilted, where is it going to go" I'm like Huh!!!!! she says"really how much shrinkage (there will be some) is going to happen and where is it going to go, once it's quilted it isn't going to end up smaller than the QUILTED quilt." hummm, so since then, I haven't pre-washed my flannel. Same concept when making a quilt top with Flannel...So no more pre-washing for me...If I think some colors will run, I will test in a small amount in water, or I will just use color catchers in the wash and through the wet catchers in the dryer with the quilt. It's worked so far...just my HMO....