Wrights also sells double fold and in various widths. And the description is that simple - single fold only has the outside edges folded in and double fold has these edges folded back in so that you can 'encase' the fabric edge. Also, if you look closely at double fold, you will see that one edge is just slightly more narrow than the other. This is the side you use on top. This helps assure that your edge stitching will catch the underside.