A seam finish stops the cut edges of a seam allowance from fraying in wear and washing, and the best one depends on the fabric more than on the garment. Serging is the fastest and suits almost everything; a zigzag does the same job on a regular machine; a French seam is right for sheers; a bound (Hong Kong) finish is the choice for unlined jackets and coats where the inside shows; pinking only works on tightly woven, stable fabric. Below is how each one behaves and which to pick for your project.
| Finish | Equipment | Best fabrics | Look inside | Durability | Time per seam |
|---|---|---|---|---|---|
| Zigzag | Any sewing machine | Light to medium wovens, knits | Functional | Good | Fast |
| Serged (overlocked) | Serger | Almost all, knits included | Neat, ready-to-wear | Very good | Fastest |
| French | Any sewing machine | Sheer and light wovens | Immaculate | Good | Slow |
| Bound (Hong Kong) | Any sewing machine, bias strips | Medium to heavy wovens, unlined jackets | Decorative | Excellent | Slowest |
| Pinked | Pinking shears | Tightly woven, stable fabric, lined garments | Plain | Fair | Fast |
Why do seams need finishing at all?
Every woven fabric is a grid of threads, and a cut edge lets the threads along it work loose. A seam allowance that frays into the stitching line fails. Knits do not fray in the same way, since loops hold each other, but their cut edges curl and can run, so they are usually finished too. A finish also makes the inside of a garment look intentional, which matters on anything unlined. The seam finish you choose is a trade-off between speed, bulk, strength and how much of it will ever be seen.
When is a zigzag finish enough?
A zigzag stitch over the raw edge, or 3 mm (1/8 in) inside it, is the standard finish for anyone without a serger, and for most cottons, linens and polyester blends it is all a garment needs. Set a width of 3 to 4 mm and a length of 1.5 to 2 mm. Stitching with the right swing of the needle landing right off the edge wraps the edge without a tunnel; on light fabric, stitching slightly inside the edge and trimming next to the stitching avoids the tunneling that a zigzag causes on the very edge.
The three-step zigzag, if your machine has it, is a better choice on fine fabric and on knits: three small stitches per swing keep the edge flat instead of rolling it. A zigzag finish is what most of the steps in finishing seams without a serger use, and it is the one to learn first.
Its limits: it is slower than serging, it is not very pretty, and on a loosely woven fabric such as a coarse linen the threads can still slip out between the zigzags after many washes.
Is a serged edge the best seam finish?
For speed and reliability, yes. A serger trims the edge and wraps it in three or four threads in one pass, at twice the speed of a sewing machine, and the result is the finish inside most ready-to-wear. A 3-thread overlock finishes the allowances of a seam sewn on the regular machine; a 4-thread overlock sews and finishes a knit seam at once.
A serged edge is the default for knits, for quilting cotton, for garment linen, for trousers and skirts in twill and for anything in a hurry. It is a poor choice on sheer fabric, where the thread shows through as a dark line, and it adds a little bulk and stiffness that can show on fine silk. If you are weighing the purchase, serger vs sewing machine covers what a serger does that a sewing machine cannot.
When should you use a French seam?
A French seam is a finish and a seam in one: the raw edges are sewn inside a second, narrow seam so nothing is exposed. It is the right choice on chiffon, voile, organza, lawn, lightweight silk and viscose, on unlined blouses and dresses in those fabrics, and anywhere a serged or zigzagged edge would show through to the outside.
It takes two passes and two pressings, and it only works on fabric light enough to fold twice without a ridge. On medium-weight cotton the enclosed seam shows as a bump on the outside after pressing, and on curves tighter than an armhole it puckers. Keep it for straight seams and shallow curves in fine fabric, and finish armholes on the same garment with a narrow zigzag or binding.
What is a bound (Hong Kong) seam finish?
A bound finish wraps each seam allowance in a strip of bias binding: the strip is sewn to the right side of the allowance, folded over the edge and stitched in the ditch from the front, so the back of the strip stays raw but is caught by the stitching. A Hong Kong finish is the version with the back left unfolded, which keeps it thinner; a fully enclosed binding has both edges turned in.
It is slow, since every allowance is bound separately before the seams are pressed open, and it adds a strip of fabric to every edge. It is also the best-looking finish there is, which is why it is used on unlined jackets and coats, on couture skirts and on anything where the inside is part of the design. Use lightweight silk or cotton lawn bias for the strips, cut 2.5 cm (1 in) wide, or ready-made bias tape in a contrasting color.
Does pinking actually stop fraying?
Partly. Pinking cuts the edge into a zigzag so the threads along it are short and lie at an angle, which slows fraying but does not stop it. On a tightly woven, stable fabric such as cotton sateen, gabardine or a firm wool, a pinked edge inside a lined garment lasts the life of the garment. On a loose linen or a quilting cotton that is washed every week, it frays back to the stitching within a season.
Pinking is quick and adds no bulk, which makes it useful on the allowances inside a lined jacket, under a facing, and on fabrics where any stitched finish would show as a ridge. A row of straight stitching 6 mm (1/4 in) from the edge before pinking (a stitched-and-pinked finish) roughly doubles its life. It is also the finish of choice on vintage patterns, where the instructions assume it.
How do you choose a seam finish by fabric?
- Sheer or very light wovens (chiffon, voile, organza): French seam. On armholes, a narrow zigzag or a bound edge in self fabric.
- Light wovens (lawn, lightweight linen, crepe de chine, viscose): French seam for an unlined garment, serging or a three-step zigzag otherwise.
- Medium wovens (quilting cotton, poplin, chambray, medium linen): serging or a plain zigzag. Flat-felled seams on shirts if you want extra durability.
- Heavy wovens (denim, canvas, twill, wool coating): serging, a bound finish for an unlined jacket, or pinking under a lining.
- Knits (jersey, interlock, French terry): 4-thread serging, or a narrow zigzag with the seam itself sewn with a stretch stitch, as in sewing knit fabrics on a regular machine.
- Fabrics that show press marks (velvet, satin, some wool): a bound finish or a Hong Kong finish, pressed over a cloth. Avoid a zigzag, which ridges.
Whatever you pick, finish the allowances before the seams are pressed open where the construction allows, and test the finish on a scrap pressed the way the garment will be: the ridge a finish leaves on the outside is the thing you cannot undo.
Which should you choose?
- No serger, most projects: zigzag or three-step zigzag. It is reliable, invisible once pressed, and good enough for a lifetime of garments.
- A serger and a busy sewing schedule: serge everything except sheers. Set the stitch width narrower on light fabric and test the tension on a scrap.
- An unlined blouse or dress in fine fabric: French seams, with a narrow zigzag or binding at the armholes.
- An unlined jacket, a coat, a skirt whose inside you will see: bound or Hong Kong finish. Budget an extra evening for it.
- A lined jacket in a stable wool, or a vintage pattern: pinked, or stitched and pinked, under the lining.
- A beginner on a first project: zigzag now, and come back to the others once a plain seam is routine.
The sewing guide that comes with each Sewly pattern tells you which seams are enclosed, which get finished and in what order, and you can ask it which finish suits the fabric you have chosen.