Mini Tutorial: How To Sew A double folded hem
1. Start by folding the hem allowance edge once at about 1/4" and iron as you fold to crease. In this example, the total hem allowance is 1". You can use a gage pointer or a ruler to ensure you are folding evenly throughout.
2. Once the initial fold is ironed and creased along the entire edge, fold again at the remaining hem allowance (3/4"). If your hemline is not directly marked on the fabric, sue a gage pointer (shown above) or a ruler to ensure you are folding the correct distance.
3. As you fold the second time, iron the double fold and insert pins perpendicular to the edge to secure the folded hem allowance layers.
4. To complete the double folded hem finish by machine: from the garment's wrong, topstitch next to the open fold following the folded edge as a guide. Remove each pin as you approach it- never stitch through the pins.
If you find that pins do not provide enough stability in the machine stitching process, especially if working with flimsy fabrics, use a temporary hand basting stitch to keep the folded layers more secure in the topstitching process.
If you stitch form the garment's wrong side and follow the folded edge as a guide, the resulting topstitch finish will naturally be applied evenly along the entire hem edge.
If you prefer not to have a visible topstitch on the garment's face side, you can use a slipstitch to permanently seal the folded edges in a blind stitch application. Simply stitch through the hem's folded edge then catch 1-2 threads from the wrong side of the garment surface, then continue to alternate the stitch in this manner until the double folded hem finish is complete.
If applied, a slipstitch application provides an invisible stitch finish on both sides of them, especially the hem's face side. This type of blind finish is often used with most tailored designs or heavier garments like jackets, blazers and coats.