I sew Warm & Natural batting pieces together after overlapping the edges that will be sewn together and cut a straight line thru both pieces. I pin the entire seam by overlapping just enough to hold the pin with the sharp tip of the pins facing the needle. I use a three stitch zigzag stitch over the butted edges created after pulling the pins out just ahead of the needle. This makes a smooth join that cannot be detected by touch either before or after quilting. The draw-back to this method is that machine sewing batting pieces together creates ALOT of lint in the needle bar, feed dog and bobbin areas!