Saturday, December 15, 2012

Professional Seam Finishes Series #3: Flat-felled Seam, Two Ways

Flat-felled seams are traditional seam finishes for jeans.  These days many of the seams in jeans are just serged, pressed to one side, and topstitched, but it wasn't always this way.  Flat-felled seams are the traditional finishing method because they are very strong, and finish out flat with no exposed edges.  They do create some bulk, especially at the hem, but they are an easy seam finish that gives great results.  They are still used most of the time on the side seams of men's dress shirts.  My personal favorite way to sew them is actually inside-out, which I use almost all the time on side seams of shirts that I make for myself.  I'm currently working on making two skirts for my little girl, one denim and one pink corduroy.  I'll be showing standard flat-felled seams on the denim skirt, and inside-out flat-felled seams on the corduroy skirt.

Advance apologies: my camera didn't like taking really focused pictures of denim, so many of the denim pictures are slightly fuzzy.

1.  For a normal flat-felled seam, start  by sewing your fabric WRONG sides together with a 5/8" seam allowance.  Backstitch at both ends.  You can barely see my thread below--it's pink.  An inside-out flat-felled seam is exactly the same, except you start the normal way with your fabric right sides together.

2.  Trim the seam allowance of the back piece if this is a vertical seam or the bottom piece if it is a horizontal seam down to 1/4".  You can eyeball this measurement as just more than half of the seam allowance width.

Inside-out version: fabric right sides together, back seam allowance trimmed to 1/4".

3.  For both versions, press the seam allowances toward the back, over the trimmed seam.
 Be careful, especially on the inside-out version, that the other side of the fabric is really flat and doesn't have any bumps in the seam.  If it isn't truly pressed flat on the right side of the fabric it can look a little off when you're finished.

4.  Use your fingers to tuck the longer, top seam allowance around and under the shorter one.
 Both of these pictures show this partway done.  Do a few inches at a time and press as you go to hold in place.

Add pins to hold everything in place as you sew it.

For the inside-out version, it is actually slightly better if you put your pins on the right side of the fabric.  I failed to do that on mine, and it turned out okay. You want the outside of the seam to look best, so it's a good idea to pin and sew from that side if you can.  

5.  Sew 1/4" away from the first line of stitching, folding down the fold of the seam allowance.  This should be just shy of 1/8" inside the folded edge.  Hard to really tell in the photo where my folded edge is, sorry.

The finished view!  Two rows of stitching on the outside of the garment: a very strong, durable seam.

For the inside-out version, try to sew from the right side of the fabric if you can.  If you aren't comfortable doing that (you might sew off of the edge and not catch the fold) it is okay to sew from the back side.  This is what it looks like finished on the inside:

Here's what it looks like on the outside.  You can see the original seam and one line of stitching holding everything in place.

It may seam like this method takes a long time, but it actually can go quite quickly, especially on short seams.  Taking time to finish a seam properly will increase the quality and life of whatever it is sewn into.


  1. Thank you for the Tutorial. Eventhough my mom taught me to sew, I don't know all the "lingo" which leaves me with a question. Is it the top stitching that makes this different than a "French Seam" on heirloom sewing projects? Thanks.

    1. That's a good question. This seam is actually very different than a French seam. A French seam starts with wrong sides together like this one, but is only stitched at 1/4", then turned right sides together, then stitched again, leaving an enclosed flap of a seam allowance on the inside of the garment. The flat-felled seam starts with wrong sides together sewn at 5/8", then wraps one seam allowance around the other, still on the outside of the garment, and finishes totally flat with no flaps anywhere. The topstitching is a part of what makes it different, but it is used in quite different applications as well. Flat-felled seams are much sportier, while French seams are dressier. With French seams you don't actually see any stitching on the outside, but with a regular flat-felled seam (not inside-out) you see two lines of stitching.

      I did a tutorial on French seams too if you're interested.

      I also do my French seams narrower than some people, a lot of people sew the first seam at 1/4" and the second at 3/8". I sew mine at 1/4", trim to 1/8", then sew at 1/4" again. I feel like this has a much cleaner finish.

      I hope this makes sense! Please let me know if you have any other questions.


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