A Hong Kong seam finish wraps each seam allowance in a strip of lightweight bias-cut fabric. Cut strips 2.5 cm (1 in) wide on the true bias, sew one to each allowance right sides together 6 mm (1/4 in) from the raw edge, press the strip over the edge to the underside, and stitch in the ditch from the top to hold it; the strip's underside is left raw, because bias does not fray. It is the finish inside unlined jackets, wool trousers and heavy coats, where it looks clean and adds almost no bulk.

What is a Hong Kong finish and how is it different from a bound seam?

Both finishes wrap the raw edge of a seam allowance in fabric. A bound seam uses ready-made double-fold bias binding, folded on both edges, and is stitched once through all layers; it is quick but stiff, and both folds show. A Hong Kong finish uses a single flat bias strip, sewn on in two passes: the first attaches it, the second secures it in the ditch of the first seam. Only one fold shows, the raw underside lies flat, and the result is thinner and more supple. It is the seam finish tailors use when a garment will be seen inside out: an unlined jacket, a coat, a vest, or the raw edges of a facing.

What do you need for a Hong Kong finish?

  • A lightweight fabric for the strips: silk organza, cotton lawn, a Bemberg or acetate lining, or a fine silk. It should be lighter than the garment fabric, prewashed, and either matching or deliberately contrasting.
  • A pattern with 1.5 cm (5/8 in) seam allowances. Narrower allowances can be bound too, but the strip then covers most of the allowance and intersections get bulky.
  • Rotary cutter, mat and a clear ruler with a 45° line, or long scissors and chalk.
  • An iron, a tailor's ham for curves, and an edgestitch foot if you have one.
  • Thread matching the strip fabric. The stitching in the ditch sinks into the seam, but the first row shows on the strip.

How do you cut bias strips for a Hong Kong finish?

Fold the strip fabric so the crosswise grain lies on the lengthwise grain; the fold is the true bias at 45°. Cut along the fold, then cut parallel strips 2.5 cm (1 in) wide. For 1 cm allowances, cut 2 cm (3/4 in) strips. Each seam needs two strips, each the length of the seam plus 5 cm (2 in), one per allowance.

To join strips, lay two ends right sides together at a right angle, sew diagonally across the overlap and press the join open. A square of fabric 50 cm (20 in) on a side yields roughly 8 m (8 3/4 yd) of 2.5 cm strips, enough for a jacket. The bias binding calculator gives the length you can cut from any piece.

The strips must be on the true bias. Strips cut on the straight grain fray along the raw underside and refuse to turn around a curve.

How do you sew a Hong Kong finish step by step?

Sew the garment seam first, at 1.5 cm (5/8 in), and press it open. Then finish each allowance separately. Keep the rest of the garment folded out of the way, and work with the allowance lying flat on the machine bed.

  1. Lay a bias strip on the right side of one seam allowance, raw edges together, with 2.5 cm (1 in) of strip hanging past each end. Do not stretch the strip; let it lie slack, which is what allows it to turn the corner over the edge.
  2. Sew 6 mm (1/4 in) from the raw edge, through the strip and the allowance only, with a stitch length of 2–2.5 mm. Sew with the strip on top so you can see it staying flat.
  3. Press the strip away from the allowance, then over the raw edge to the underside of the allowance. The seam you sewed is now at the very edge; it helps to press this fold over the edge of a ruler or a card.
  4. Stitch in the ditch from the top: with the allowance right side up, sew exactly in the groove of the first seam, catching the strip underneath. The stitching disappears into the seam. An edgestitch foot with its blade in the groove keeps you on the line.
  5. Trim the strip's underside to 6 mm (1/4 in) from the ditch stitching, or a little less, with the allowance folded back so you cannot cut the garment. The raw edge of this bias is left as is.
  6. Repeat on the other allowance, then press the finished seam open over the ham from the wrong side, and press again from the right side with a pressing cloth.

The band that shows on top is 6 mm wide. For a narrower band, sew the first row at 5 mm (3/16 in); for a wider, more visible band in a contrast color, 8 mm (5/16 in) and strips cut 3 cm (1 1/4 in) wide.

Should you bind the allowances before or after sewing the seam?

After, in general. The seam is pressed open first, so each allowance lies flat and you can see exactly where the band falls, and seams that will be trimmed or adjusted during fitting are not bound in vain. Binding before sewing the seam works on straight seams whose fit you trust, such as a center back seam or the long seams of a coat; it is easier to handle, because the pieces are still flat and you are not wrestling a whole jacket under the needle. Whichever you choose, do all the seams of a garment the same way.

For seams pressed to one side, such as a skirt's side seam pressed toward the back, bind the two allowances together as one, which uses half the strip.

How do you handle curves, corners and crossing seams?

On a curve, the strip follows because it is bias. Hold it slack as you sew the first row, and press over the ham so the band follows the curve. On an inside curve such as an armhole, clip the allowance at 2 cm (3/4 in) intervals inside the band only after binding, and the band keeps each clip covered.

Where two seams cross, bind the first pair of allowances the full length, sew the crossing seam, then bind its allowances over the bound ends. Trim the allowances under the bands to 1 cm (3/8 in) at the crossing to keep it thin. At a hem, stop the band 1 cm above the hem fold and finish the band's end inside the hem.

For the edge of a facing, the band runs along the outer edge of the facing in exactly the same way, which is one of the nicest finishes in an unlined jacket.

Common mistakes with Hong Kong finishes

  • Strips cut off grain. They fray along the raw underside and the band ripples. Check the 45° with a ruler before you cut.
  • Stretching the strip while sewing. The band comes out narrower than planned and the seam puckers when the strip relaxes. Feed it loosely.
  • A band of varying width. The first row was not a constant 6 mm. Use the edge of the foot or a tape guide, and do not trim the allowance beforehand, because the raw edge is your guide.
  • Missing the strip with the ditch stitching. The fold was not pressed fully over the edge. Press after step 3 and check from underneath before you sew.
  • A strip fabric heavier than the garment. Bands in a mid-weight cotton stand up stiffly on a drapey wool. Go lighter.

If you draft with Sewly, the sewing guide lists the garment's seams in the order you sew them, and you can ask it which ones will be visible inside an unlined garment so you know where a Hong Kong finish is worth the time.

When should you use a Hong Kong finish instead of serging or a French seam?

Use a Hong Kong finish on unlined garments in medium and heavy fabric: jackets, coats, wool trousers, vests, and on facings and waistbands where the inside will be seen or will rub against the skin. It is slow, so reserve it for garments that deserve it. Serging or zigzagging is faster and better on fabrics you will never see the inside of, and the guide to finishing seams without a serger has the quick options. On sheers and lightweights, a French seam encloses the edges with less work. Seam finishes compared sets all of them side by side, and if you are weighing a Hong Kong finish against a full lining, lined or unlined is the next read.