I just finished a long table runner. Instead of batting I used felt because it lays flat and keeps its shape. I make mostly art quilts, and large ones. My last had 5 layers: top, wool batting, warm and white, felt and back -- and it hangs perfectly straight on the wall. I've been wondering if felt alone would work, and it does. For a wall quilt I think I'd add a layer of wool batting for depth, and delete the warm and white.