Understitching is a row of straight stitching that holds a facing to its seam allowance, so the facing cannot roll out and show at the edge.
It is invisible from the outside, it takes thirty seconds, and it is the single clearest difference between a neckline that looks made and one that looks home-made.
How to do it.
Sew the facing to the garment as normal. Grade the seam allowances — trim them to different widths — and clip the curve so it can lie flat. Press the seam allowances towards the facing.
Now stitch from the right side of the facing, close to the seam line, catching the facing and both seam allowances underneath but not the garment. About 2 mm from the seam.
Press the facing to the inside. It will now stay there.
Where to use it. Necklines, armholes, waistband facings, the edges of collars and cuffs. Anywhere a facing meets an edge that will be seen.
The one place it does not go is a seam that has to be pressed open flat, since understitching commits the allowances to one side.
And do not skip the clipping. Understitching a curve that has not been clipped just locks the pull in place.
Questions people actually ask
Is it the same as topstitching?
No. Topstitching is visible from the outside and decorative as well as functional. Understitching is invisible and purely functional.
My facing still rolls out.
Either it was not understitched close enough to the seam, or the curve was not clipped so the allowance is pulling. Both are fixable by unpicking and redoing.
Last reviewed 2026-08-11