How to sew an Understitch
If you've ever sewn a pocket bag or a neckline facing and you find that the inside parts keep peeking out, trying to steal the spotlight from your beautiful the garment, it's likely because you haven't sewn an understitch along the seam of the finished edge. An understitch is used along edges where you have inner linings or facings that you want to remain concealed on the inside of the garment. This stitch that will help all those inner parts to stay put, leaving you with crispy clean finished edges!
This demo illustrates the stitch with a neckline facing, but you can follow these steps for any other instance where the stitch is required. Here's how you do it...
Begin by sewing the facing to the neck of your garment at the seam allowance indicated in the pattern.
If the seam is curved, clip the seam allowance perpendicular to the edge of the fabric, making sure not to clip the stitch line.
Press the entire seam allowance towards the facing. You may press the seam allowance while looking at the wrong side, but be sure to press from the right side as well to ensure that the seam is pressed open.
Stitch a line along the facing, on the right side of the fabric, 1/8” away from the seam. You should be catching the seam allowance (underneath) as well as the facing. Be sure to continuously check the seam allowance while sewing, to confirm that it is sitting in the right direction.
Press the facing and body of garment flat, as demonstrated in the picture.
Then, fold the facing over to the inside of the garment (so that it appears like how it would be worn), and press along the finished edge. Pressing from the right side of the garment will ensure that the facing is not visible from this side.
And there you have it - the under-stitching technique ensures a clean and crisp effect along your finished edge.