I place the two pieces of batting with a slight overlap and then cut it through the overlap using my rotary cutter and ruler. By doing it this way I have two matching edges that lay flat. I usually whip stitch it by hand but have also zig zagged it on the machine too. I enjoy doing hand sewing so prefer to whip stitch it. The price of the iron on joining strips has shied me away from using them. I always use warm and natural so I can't speak for other kinds of batting. No batting goes to waste around my house.