A French seam encloses the seam allowance on the inside of a sewn item, so no raw edge is visible. This eliminates the need for another form of seam finish. It's used most commonly on sheer fabric, so the seam blends with the fabric. But it can be used on any fabric where you want to enclose the seam allowance and keep a soft edge. This works especially well for clothing if rough seams bother you. It's also helpful to join sections of fabric when making window treatments for a seam that blends into the fabric and is visually appealing from the wrong side of the curtain when it's visible from the outside of the window. Once you understand the steps, a French seam is fairly quick and easy to sew.
A French seam is most commonly applied on a straight seam. It's difficult to do on a curved seam, but this can be done if you use a very small seam allowance. Practice a curved seam on fabric scraps before sewing your actual item.
Equipment / Tools
- Sewing machine
- Iron and ironing board
Sew the First Seam
Pin the wrong sides of the fabric together where you want your seam to be, so the seam allowance will be on the right side of the fabric. This is the opposite of how you would normally sew a seam.
The general rule for a French seam is to subtract 1/4 inch from the seam allowance your pattern calls for. So if your patterns calls for a standard 5/8-inch seam allowance, sew your seam with a 3/8-inch seam allowance. Then, trim the seam allowance down to 1/8 inch.
Press the Seam
Press the seam as it was sewn. Then, fold the fabric along the seam line, so the right sides of the fabric are together and the stitching is at the edge of the fold. Press well, so you are working with a sharp crease at the fold on the seam.
If necessary, use a pressing tool, such as spray sizing or spray starch, to give the fabric a sharp edge. This will come out in the laundry, so the edge is ultimately soft.
Pin the fabric in place, especially if it's a slippery material.
Enclose the Seam and Press Again
With the right sides of the fabric still together, sew a second seam 1/4 inch in from the folded edge. Be sure this seam completely encloses the first seam, so none of the first seam's allowance sticks through. This is important because the allowance would end up showing on the right side of the item.
If the fabric is fraying, take the time to tuck those wandering threads inside the seam or trim them as you sew. Don't pull the threads because you will probably make the fraying worse.
Press the second seam as it was sewn. Then, open the fabric with the wrong side facing up, and press the seam to one side. (Press it toward the back of a garment if applicable.) Finally, flip over the fabric, and press the seam again with the right side facing up.