Voulez-vous coudre avec moi?: How (and why) to sew French seams

December 19, 2018 by scarlettsparks

Hey there, my fabulous friends! Perhaps you’ve noticed that it’s been eerily quiet around here, and that’s because I’ve been on the other side of the world taking some much-needed time off with family and friends. I’d originally planned to cram in a bunch of blogging and photography and admin work while I was away from the sewing studio (the machine tends to funnel my attention away from all other tasks when I’m within 20m of it), but in the end I barely cracked the laptop and I have zero regrets. My mind needed some time to chill out just as much as my body did.

Leading up to the trip, I pushed out a lot of sewing projects that I didn’t share many glimpses of (partly because some are part of a not-Palm line of side-hustle, partly because some are still Top Secret, partly because I barely had time to stretch my wrists, let alone write a decent IG caption), many of which just happened to feature French seams. I thought this was a great opportunity to discuss not only how to sew this seam finish, but why it’s a great technique to keep in your costuming toolkit.

Pssst… to help offset the costs of running the site and developing new patterns, I may include affiliate links from time to time (including in this post), which means that if you click the link and purchase a product I’ve mentioned, I will receive a small commission from the sale. I promise that I’ll only include affiliate links that are relevant and contextual, for things that I would have written about anyway, and I’ll always indicate which links are part of an affiliate program. For more information, please see my Advertising and Disclosure Policy.

Pardon my French, but what le heck is a French seam, and why would you do it?

A French seam, despite the name, requires no translator. It’s simply a method of sewing a seam so that the raw, cut edges of the fabric are fully enclosed within two lines of stitching, leaving a neat, narrow seam allowance that is pressed to one side. You don’t need a serger, extra lining fabric or bias binding, or any special equipment. Just time and patience! In a nutshell, you sew one pass with wrong sides together at half(-ish) the full seam allowance; then you trim close to the stitching, flip it right sides together (the usual orientation for most seams) and sew a second pass that captures the raw edges in the channel between the two lines of stitches. This makes it a great choice for finishing:

• woven fabrics that tend to fray, because the edges that would normally fray are protected inside their little seam sandwich, hiding away hairy edges and preventing friction that would make fraying worse;
• delicate fabrics that could benefit from two lines of stitching as a defence against wear-and-tear;
• sheer or translucent fabrics where the “guts” of your sewing will be on display;
• unlined garments where the insides might show and you want it to look as clean as the outside, such as:
• • skirts or dresses with long slits;
• • capes, coats, and cloaks;
• • really full, twirly skirts;
• • a garment you plan to remove.

…as in, lots of stuff we routinely put on stage, especially in burlesque, bellydance, and lots of other dance arts.

Now, even if your garment meets all of the above criteria, French seams may not be the only or best option. Several other techniques exist that could also enclose your raw edges and look hawt on the inside (eg. Hong Kong finish, felled seams, full or partial lining, etc.) that each have their own pros and cons. French seams tend to work well when you have a long(ish), not-too-curvy seam to deal with, and you want the outside to look like a totally-normal-nothing-to-see-here seam with no topstitching. It might not be ideal if:

• you’re sewing with knits rather than wovens – because the yarns interlock differently, knits don’t tend to fray like woven fabrics (though some will ravel or get ladders), plus stretch knits might be prone to bubbly or wavy seams using this construction;
• your seams are very curved – the original width of the seam allowance, and the flipping, and the two passes of stitching may make it more difficult to sew tight curves accurately and cleanly, plus pressing curves is a dilemma if you can’t clip or notch without compromising your stitching;
• you expect that the garment may need to be altered for fit in the future – unlike some seam finishes that are pressed open, you can’t leave extra seam allowance as insurance to let out the garment in the future, and even what moderate seam allowance you started with is partly trimmed away during construction of the seam, making it tough to retro-fit changes once it’s all together;
• you need minimal bulk at the seams – you’ll end up with almost four layers of seam allowance all pressed in the same direction, which could be a downside in very tight-fitting garments or with bulkier fabrics;
• you aren’t confident stitching small (1/4″ or 6mm) seam allowances accurately.

Also note that just because you choose to use French seams in one part of a garment, that doesn’t mean you have to commit to using them for everyseam. You can totally evaluate this on a seam-by-seam basis.

OK, I’m sold, but how do I do it, s’il vous plaît?

(First: an apology. I had loads of pictured prepared to help you visualize each step below, but WordPress changed some interface features while I was off romping with the kangaroos, and, (amongst other things, like losing seamless Markdown integration, cue endless swearing) after three (THREE!) days of trying fruitlessly to get images to show up in the correct place at the correct size, I must resign myself to one measly photo or risk never posting anything at all. I hope to update this post Soon™ with the missing images, or at least a supplemental video. In the meantime I hope you can make sense of my jet-lagged prose.)

Step 1

Check whether your pattern calls for either 1/2″ (12mm) or 5/8″ (15mm) seam allowances in the area where you’re planning to use French seams. If it calls for a smaller seam allowance, like 3/8″ or 1/4″, that might be a sign that this area is not a good candidate for this construction method; however, if you’re sure you want to forge ahead, you’ll need to re-draw the seam allowance so it equals a total of 1/2″ (12mm) (or 5/8″ if you prefer).

Step 2

Place your pieces wrong sides together. You eventually want your second pass of stitching to be sewn at 1/4″ (6mm) from the first, so subtract 1/4″ (6mm from your starting seam allowance), ie.:

• if you are starting with 1/2″ (12mm) seam allowances, stitch your first pass 1/4″ (6mm) from the cut edge);
• if you are starting with 5/8″ (15mm) seam allowances, stitch your first pass 3/8″ (9mm) from the cut edge.

Step 3

Trim the raw edge to about 1/8″ (3mm) from your first line of stitching, making sure to cut away any fluffy frays. This ensures none of the raw edge will get caught in the final seam that would show on the outside of the garment. Be careful not to clip through any of your stitches, and try to avoid trimming too close to them.

Step 4

Flip and press this teensy seam so that the raw edge is sandwiched between the pieces, which are now right sides together as usual. Depending on your fabric, you may find it helpful to press the seam flat to one side first, before flipping it and pressing that crisp edge.

TIP: use a silk organza press cloth ($) over your delicate fabrics to prevent scorching or melting; silk is a natural fibre, so it won’t melt, either, and organza is sheer, so you can still see what you’re doing! 

Step 5

That’s it!

You’re done! Admire your beautiful garment guts, ready for their stage début!