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 them so they show on the right side, as a decorative effect !

(Oddly, the French call this technique ‘English seams’ – coutures anglaises !)

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 – inward curve – no problem

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 – outward curve – needs special technique

The second stitching line is shorter than the first. A French seam like this can distort the fabric.

Worth trying some samples with your fabric. If you can’t get a good result, 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.
– after sewing the first stitching, trim the seam allowances to 1/16″ round the curve, 1/8″ elsewhere.
– 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 !

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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 as elegant as a true french seam, but good to know.

Start by sewing right sides together as for an open seam.
Then fold in the edges, and sew the folds together.

Here are a couple of videos :

Professor Pincushion
This includes a french seam, but less detailed than the previous video.
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 much more elegant seam finish.

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Written April 2014, links revised August 2019

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