I've made TONS of flannel quilts- you will get lots of responses here- from people who insist on washing their flannels 3 or 4 times before using them- to ones who always wash at least once- to ones who do not wash them at all. I have made lots of quilts that had regular cottons and flannels in the same quilt top= some washed, some not- they have always turned out just fine. my 'decision' on handling flannels is this- if it is a good quality double sided flannel unless I am worried about the color bleeding I do not always pre-wash it. if it is thin, loosely woven, lesser quality I wash it- in hot water, and dry it in a hot dryer- I want to tighten up that weave. if it feels funky, or smells funky, I wash it- if it is 'meaty' (as in heavy, luxurious) I do not pre-wash it. I learned many years ago to not stress over this kind of stuff- if its thin, cheap, loose, yukky- wash it. if its nice quality, soft, heavy, tightly woven- don't worry about it.