I used a flannel blanket for a bargello QAYG recently. The pattern called for it because some of the strips finished at only 1/4" wide and anything thicker would have not allowed the pattern to show as well. It worked great.
For a quilt, it would work well also, just remember that it would not be as "fluffy" as one with batting.

In the old days, our foremothers did NOT have batting!! So they used what they had. Some quilts didn't even HAVE batting --- usually for climates that got hot.

I think I'll try flannel on my next scrappy quilt!!! I KNOW I plan on doing a flannel backing!

I made one of these in soft baby print for grandson born in Phoenix in the summer! It was perfect. Protected him from AC but could be thrown in the bag easily when not needed.

Your right, flannel makes a wonderful batting, particularly for throws. We put three pieces of flannel together and if is great.

Flannel works just like a low loft cotton batting. In fact if I see a good quality flannel sheet at the thrift shop I snap it up, usually for a dollar or two. I use them all the time in all kinds of projects, as for the pieced backs....I do that all the time, usually I try to incorporate left overs from the top...it is like getting two quilts for the price of one. It adds fun to scrappy and kids love the idea.

Could you use no batting and just a flannel backing? Or if you use the flannel for batting, what do you use for backing on top of that?

I use it in my baby quilts so they won't be so heavy, of course I use minky on the backs and that adds weight too

Wow! Never thought about flannel as batting before. Can't wait to try it.

Just got done cleaning guest room for visitors over Xmas and found 3 poly blankets I forgot I had. Also took the blanket off the guest beed and put on a down comforter so have another blanket. Thanks for reminding me that they will also work.

I've used flannel for batting in quilts and runners. You can also use it for the backing. Works really good.