The french seam is an enclosed or ‘self-finished’ seam – no exposed seam allowance edges.
Here are some comments on sewing a :
– straight french seam,
– french seam round a curve,
– mock french seam.

photo from the former Craftsy site

French seam especially used for :
– garments which touch the skim, such as lingerie, to minimise rubbing of the skin.
– transparent/ sheer fabrics, so the seam allowances can’t be seen.
– heavily fraying fabrics, to protect the fabric edges.
You can even sew french seams so they show on the right side, as a decorative effect !

(Oddly, the French call this technique ‘English seam’ – couture anglaise!)

How to do it

The thing which can really confuse is that french seams start with sewing fabric ‘wrong’ sides together.
Then trim, press open, turn, sew with right sides together, and press again.

Here are a couple of written tutorials :
Tilly and the Buttons

Here’s a video on sewing a french seam :

Each tutorial uses different measurements, trimming and pressing techniques. These things are not set in stone ! It’s the general principle that counts. Choose which you are happiest with, and which best suits your fabric and application.

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French seam round a curve

The trouble with many enclosed seam methods is they’re a problem to work round curves without distorting the fabric.

With a curved french seam, the 1st stitching line and the 2nd stitching line are different lengths.
Here’s 2 different situations.

1. Armhole seam or crotch seam – in wear the finished seam allowances make an inward curve – no problem.

The cut edge is shorter than the first stitching line. So you will need to clip through the seam allowances after the first stitching. But not to worry as those little clips will all be enclosed by the second stitching.
The first stitching line is shorter than the second. Unlikely to cause a problem, as the shorter first stitching line is naturally in a shorter position in wear.

Here’a photo tutorial from Grainline Studio on how to sew a french seam around an armhole.
And here’s a video about sewing a french seam at armhole, from Made to Sew.

A crotch seam on pants is similar.

2. Underarm seam of cut-on sleeve – in wear, the finished seam allowances lie in an outward curve – needs special technique.

In this situation, the second stitching line is shorter than the first. Easy to sew, but when it’s turned right side out in wear it does not work so well. A French seam like this can distort the fabric.

Worth trying some samples with your fabric. If you can’t get a good result, one possibility is to sew an open seam round the curve, and clip the seam allowances so they can be pressed flat. But that method can never give a tidy result inside a garment.

I did some experimenting, and found it is possible to sew a french seam round a curve without too much fabric distortion.
– only try this round a curve of at least 3″ (8 cm) radius. Smaller curves will distort the fabric. Use a shorter stitch length round the curve if your fabric needs more support. If your pattern has a very extreme curve, you may like to change the curve to one less extreme.
– after sewing the first stitching, trim the seam allowances to 1/16″ round the curve, 1/8″ elsewhere. Double the stitching round the curve, if you feel it needs more support.
– sew the second stitching only 1/8″ away from the edge around the curve. You can extend the width to 1/4″ on the straight sections.

These tests were done in muslin. Try some samples in your own fabric before doing it for real ! A more loosely woven fabric may be easier to get a good result. With a tighter woven fabric, you may need to use an even wider curve.

Some people say you can get a better result with a mock french seam, as in the next section, but I haven’t found that myself.

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Mock French seam

photo from A Fashionable Stitch

If you make a mistake and start your intended french seam by sewing right sides together, no need to panic and unpick – just turn it into a mock french seam 😀

Not quite as elegant as a true french seam, but good to know.

Start by sewing right sides together as for an open seam.
Then :
– open apart the seam allowances,
– fold in the edges to the central seam,
– and sew the folded edges together.

I find the folding in is slow and fiddly, though the result is neat. It can be a useful thing to know how to do.
Easiest to do the second stitching using a straight stitch and an edge stitch foot.

Here are a couple of videos :

Professor Pincushion
This includes a french seam, but less detailed than the video above.
Mock french seam starts at 4.05.

Here’s another video with a slightly different perspective :

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Both french seam and mock french seam are good techniques to know. Many people think these methods are too much trouble in this serger/overlocker age, but they :
– do make a more elegant seam finish, if you like the inside of your garments to look special.
– are essential for a quality final look with transparent or sheer fabrics.

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Written April 2014, links revised September 2021

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