Prism99

My advice is no, do not preshrink the batting. It will shrink no more than 3% and give a nice softness and crinkled look to the flannel.

Once fabric is quilted to batting (in a moderate fashion, where no more than 3" or so in area is unquilted), the batting controls shrinkage. In other words, at that point the fabric cannot shrink so much that it pulls at the batting; the tension that the batting provides will keep the fabric from shrinking more than the batting shrinks.

If you absolutely do not like the crinkled look in a quilt, then you would need to preshrink the Hobbs 80/20. Honestly, though, I would not do that.

Edit: I once attended a workshop given by Harriet Hargrave. She brought with her a flannel quilt to prove that it is not necessary to prewash even flannel in order to control shrinkage. The quilt was made entirely of unwashed flannel fabric and quilted to Hobbs 80/20. She measured the quilt before and after washing, and it shrank exactly the amount of the batting (about 3%).

I think a lot of quilters do not realize that fabric shrinks differently when washed by itself as opposed to after having been quilted moderately to batting.