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Machine Sewn Seam Finishes - French Seams - Part 2 of 4

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A number of years ago, we had a French intern working with us... the daughter of a friend of a friend - you know how those things go. She was a sweet girl with a lovely accent, and we had fun asking her for the translation of things we tag as "French": a French braid to her was an Indian braid; French cut was Brazilian cut; French fries were American! We didn't get into all the amazing sewing techniques influenced by fine French (or heirloom) sewing. There's the French cuff, French dart, French knot, French curve, French binding and today's topic: the French seam. Ready to give it a try? Wearing a beret is optional.

The French seam, which is part two in our series on Machine Sewn Seam Finishes, is one of the best finishes for a variety of sewing projects. Unlike part one of this series, in which we explored the most popular types of seam finishes you can do using a variety of built-in stitches on your sewing machine, in today's tutorial, we look at how you can use just a basic straight stitch to create a professionally finished seam inside and out.

In general, the purpose of any seam finish is to prevent fray-prone fabrics from raveling beyond the seam and leaving a hole in your sewn project. However, regardless of fabric type, finishing a project's inside raw edges will not only elevate the final appearance, it will also elevate your sewing skills to a professional level. 

Deciding when and where to use a French seam is fairly simple. If a fabric is sheer and/or delicate, it’s an ideal candidate. Heavyweight fabrics can be used but are a challenge because of the bulk of the seam. As with all techniques, it always best to test the French seam on scraps to determine if it’s truly the best finish for your fabric type. In general, light to medium weight fabrics are perfect for a French seam finish. 

We will warn you this technique may appear to be a bit of a brainteaser to execute, but it’s actually very easy. Once you’ve given it a try, you’ll be so happy you did. The result is worth the extra steps.  

One other note of caution, the French seam technique is best used on straight seams. Curved situations, such as a set-in sleeve in a garment, are finished using a different seam finish (hang in there... we have four parts to this series!).

Tools to have on hand

Understanding the seam allowance measurements

As we mentioned above, the French seam can seem confusing at first because it’s a two-step seaming process: first you sew with wrong sides together, then with right sides together. Anyone who is an avid sewer will immediately feel they’re doing something gravely wrong by placing the fabric wrong sides together. But, fear not, as we go through the steps and explain the seam allowances, you will see why this works so well.

We always like to review the standard seam allowance measurements for the type of projects you may want to sew. In home décor, the general seam allowance is ½", whereas in garment construction, it’s ⅝". (You would not apply this seaming technique in quilting.) 

Since the French seam technique is based in garment sewing, we will first explain how this seam allowance is divided in the two-step process. In step one, you sew a ⅜" seam wrong sides together. The seam allowance is trimmed to ⅛" from the line of stitching, which means you are trimming away ¼". In step two, the fabric is placed right sides together along the previously sewn seam, and sewn with a ¼" seam allowance, enclosing the raw edges of the first seam. Confused yet? The important part to understand here is that the total seam allowance of ⅝" is maintained, ⅜" + ¼" = ⅝". And you thought you’d never use those pesky fraction lessons from fourth grade! 

Now, if you’re working on a home décor project, using a ½" seam allowance, it's best to add ¼" to all the cuts where you’ll be applying the French seam technique, giving yourself a ¾" seam allowance. Why? Because you need that little extra to complete the process, otherwise you'll be working with very tiny seam allowances.

Whether you’re following a pattern or designing your own project, take a few minutes to consider if you need to add a little extra to the seam allowance to accommodate a French seam finish. Once you practice and become familiar with the technique, these tiny seams won't be an issue, but if you're just starting out, give yourself a bit more fabric with which to work.

Basic Steps

As if the French seam isn’t confusing enough already for most folks, there’s more than one way to complete the seam: the traditional way and an alternate that has evolved over time. The final product is quite similar, so we encourage you to try both to find your favorite. 

Traditional method

NOTE: For this method, we are using a garment seam allowance of ⅝". We are also using a contrasting thread so you can see the stitching clearly on the fabric. You would use a thread color to match your fabric.

  1. Set up your sewing machine for a straight stitch, with the appropriate needle and thread for your fabric type. 
    NOTE: If your sewing machine has a Cloth Guide, as many of our Janome studio machines do, this is the perfect time to use it. Maintaining accurate seam allowances is key to this technique.
  2. Place your fabric wrong sides together. Pin as needed.
  3. Sew a ⅜” seam along the raw edge.
  4. It's just a plain seam. See... nothing to be afraid of.
  5. Trim back the seam allowance to ⅛", trimming away to ¼". Why stitch then trim? So the fabric fibers do not poke through the final seam.
  6. Press the seam allowance together and to one side. This is an important step so don’t skip it! Pressing the seam flat helps to maintain an accurate seam allowance and will makes it easier to sew along the seamed edge in the following steps.
  7. Now, fold the fabric right sides together. Your sewn seam becomes the new edge of the fabric. 
  8. Press again along the edge. Lightly pin in place if needed.
  9. Sew ¼" from the seamed edge, enclosing the raw edge of the first seam as you sew. 
    NOTE: If you have a Quarter Inch Seam foot for your machine, it will help you keep an accurate seam line. 
  10. Press this second seam to one side, and admire your professional French seam finish from the inside and out!

Alternate method

The basic difference with this method is you do not trim the edge after sewing the first seam.

NOTE: We are using a home décor seam allowance of ½", so we added an extra ¼" to our seam allowance before cutting out the fabric pieces. 

  1. Set up your sewing machine in the same manner as for the traditional method above.
  2. Sew wrong sides together, using ¼" seam allowance.
  3. Press the seam allowance together and to one side.

    NOTE: We discovered some sewing blogs who mentioned they prefer to press the seam open at this step. It's a bit of a personal choice, and it depends on the fabric type.
  4. Fold the fabric right sides together. As above, your sewn seam becomes the new edge of the fabric.
  5. Sew a ½" seam allowance, enclosing the raw edge of previously sewn seam.
  6. Press to one side again. Fantastique! 

Additional tips

  • If you’re planning to use French seams on a project of your own design, remember to account for the proper seam allowance in the two-step process.
  • Before you sew the second seam in the process, you can pink the raw edges rather than simply trimming.
  • Avoid using French seams on really heavyweight fabric due to the bulk. Super stretch fabrics are not a good choice either.
  • Curved areas are best completed with a mock French seam (more info of these coming up later in our Seam Finishes series).
  • Avoid garments with set-in sleeves, as this is an advanced technique for the experienced sewer.
  • If you plan to use French seams in a home décor project and feel confident with sewing tiny yet accurate seam allowances, you can sew the first step with a scant ¼" seam, trim to ⅛", then use a generous ¼" seam for the second step. This eliminates the need to add on the extra ¼" suggested above.
  • Even if you own a serger, sometimes a fabric is simply too delicate for an overlock stitch. The French seam technique is the way to go!

If you would like to continue to build your knowledge about other seam finishes check out the following Sew4Home tutorials:

Flat Felled Seams

Understanding Understitching

Introduction to sergers

Sewing with Sheers

Machine Sewn Seam Finishes - Most Popular - Part 1 of 4

And don’t forget about those hemlines!

Simple Hem

Blind Hem

Rolled Hem

Corner Hem

Contributors

Sample Creation and Instructional Outline: Jodi Kelly

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Comments (3)

Beth T. said:
Beth T.'s picture

Thank you for this.  Pressing the seam together and to one side while it is still wrong-sides together is a step that wasn't in the directions I've been using, and I can see your way will bring so much less frustration to the process.  Once again, why didn't I think of that?  Glad to have you to do the thinking for me. 

MarciaFlorida said:
MarciaFlorida's picture

Very interesting -- something I've wanted to learn how to do.

Jane Coombs said:
Jane Coombs's picture

If you have ever had anything made in Southeast Asia, this is the seam finish used by most tailors. The part that intrigues me is the using the standard seam allowance and then trimming it. I don't think the Southeast Asian tailors do this. They take a smaller seam allowance to begin with. They have no time for trimming, or tolerance for waste.The way you have presented it is the way I was taught.(BTW, I am referring to tailors in Bali and Malaysia not the high end suit makers in Hong Kong.)

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