I use Pellon ultra lightweight fusible interfacing. I buy it in packs of 15"x 3 yards. I make my blocks 15" so it works out perfect for me (price and convenience). I use fleece backing, no batting. I 'Birth" my quilts, thev zig-zag over the seams for quilting. I use lots of pins when quilting, because fleece tends to stretch and slide. I've never tried flannel, that might be easier to work with.