I am using a wool wadding for the baby quilt, but needed to join 2 pieces to make the correct size. The cut edges are butted together & stitched using the walking foot. In the sample photo above I've stitched with a contrast thread to show the three step zigzag stitch that I prefer for this job.
The loft of the wadding buries the stitches nicely & once the quilt is fully quilted these joins are invisible.