if the flannel width and length is going in the same direction on both sides it will be better that not. if the batting wasn't washed and also shrinks some, that will help, too. but you will still have shrinkage on the flannel. since you didn't do any prep, i would never wash in hot water, if possible, only cold. only tumble dry gently and grab it out of there to finish drying in the air. if it's a gift, write everything down on the label or gift card. it will end up smaller than when it started out. good luck with it.

I just quilted a Queen sized quilt with flannel backing on my longarm. Once the flannel was prewashed and dried to get out the excess dye and shrink it, it worked fine. But, it shrinks 5%.
It was stretchier too so needed regular cotton strips attached to all sides for stabilization. With all that, it came out quite nicely.
Cynthia

About the only time I've been told NOT to wash flannel is when you are using FQs for Turning Twenty quilts, as the flannel will be too small for the cutting instructions. (That info came from the gal who conducted the TT class I took.)

I agree with all of the above, but it does tend to stretch more than cotton broadcloth, so use lots of pins when you put it together or hand baste the heck out of it.

Flannel is usually a little bit narrower than a flat cotton. It is a looser weave, too so be sure to prewash and shrink it before you use it. Flannel makes a cozy quilt and I love it with a cotton batt like Warm and Natural.

Can you hand quilt with flannel on the back? Hubby really wants a flannel backed quilt, but I don't know if it would quilt well.

Flannel is one fabric that I will only buy at my lqs. I have made pj's out of it for my DGS's and some of them are 10 years old and are now being worn by the fifth one. They are starting to fade, but are so soft and cuddly.

they handquilt wonderfully well.

they stretch like mad, but pull back in with each washing.

before you wash, finish the edges very carefully or they'll fray so badly you won't have nearly as much as you need, so overbuy.

they get softer and softer with age.

there are various qualities - some quite poor. buy carefully and touch it first.
hold it up to the light and look at how thin it really is. it's hard to tell with all the sizing they put on it. the thin ones do not hold up.

Thanks for the help. Not a gift, it's for me so no matter what I won't mind too much. I always wash in cold so that is not a problem either. The quilt is so large it won't matter if it shrinks a bit actually. If it is not horrid, I will post pictures, been working on this thing for about six years, yikes! Thanks again!

I might just have to get a flannel to back it with if it handquilts well. I kinda know what NOT to look for. Do you have qualities that you do look for when you look for a flannel? I'm assuming thicker is better...I just want to make sure I can still quilt through it....but I know he would really love it if I put flannel on the back.