When I split the batting into thirds, I found the easiest way to re-attach is to butt the batting pieces together (this is where the registration marks are invaluable!) and use the iron-on tape. I have also used strips of fusible nylon tricot. (This might even be what the commercial strips are made of; I'm not sure.) There is no overlapping -- just butting. I have also done machine zigzag, but I think the iron-on strips are easier.