I used a stack of 10 inch squares layer cake that were good quality Woolies flannel, and I had Woolies yardage for sashing, setting and backing. I decided not to prewash because I could not do so to the layer cake, but on the advice of several online videos and articles I did use spray starch to stabilize the precuts. I was shocked to watch the flannel squares shrink before my eyes when the starch hit them (even before ironing) and many lost up to a half inch on a side or were no longer square. I had to revise my entire pattern measurements because I could no longer use the entire square as I'd intended. Unless I'm using precuts, I will always wash and dry flannel, no matter what the quality.

I have had that experience with any quilt….when I first started longarming…..I kept a notebook and put down the finished size of the top before quilting, the size after quilting.....and the size after the first washing and drying....yikes....it really was pretty common for the quilt size to shrink by 2-4 inches from the quilting and then again from the washing...these were mostly full sized quilts....

I always wash my flannels before using for quilting, although I do not buy the expense flannel.

Always
Prewash
Flannel!!

For giggles one time I measured before and after - 4 inches of shrinkage over WOF. Lots o lint came off too - better in wash than under my bobbin case!

Note- this was cheap JAF "snuggle" but that stuff was SOOOO SOFT. Awesome for babies.

I wash and starch all flannel before cutting.

I prewash anything that is black. It would be a shame if the color ran after you made the quilt.