understitch

Understitching is a sewing technique used to secure a garment’s facing or binding to the seam allowance so that the edge lies flat and the facing remains inside the garment. The goal is to prevent the facing from rolling to the outside and to create a cleaner, more durable finish.

The technique is typically applied after attaching a facing to the main fabric along a seam. With the garment oriented so the facing is inside, a line of stitches is sewn very close to the edge of the facing, catching the seam allowance as you go. This stitch line is usually a short, fine seam, placed about 1–3 millimeters from the edge, and should go through the facing and the seam allowance but not through the outer fabric. Backstitch at the ends to secure the thread.

When to use it: It is most common for necklines, armholes, and waistline facings, as well as other bound edges where a clean, low-profile finish is desired. It can also be used with linings and other internal bindings to prevent edges from curling outward.

Variations and tips: For curved edges, carefully grade or clip seam allowances to reduce bulk and ensure a smooth roll. Use a fine needle and thread, and trim excess seam allowance before understitching. If a visible finish is preferred, topstitching along the edge can achieve a similar effect, though it is not identical to understitching.