August 25, 2022
by Cynthia Anderson
Like French seams, flat felled seams encase the raw edge of the seam allowance creating a strong and clean finish that prevents fraying. Flat-felled seams are a typically found on clothing for men, children, and sportswear because of the strength and durability of the seam construction. If you own a pair of jeans, they are most likely have flat felled seams.
Depending on the look you want, flat felled seams can be made to appear on the right or wrong side of a garment. This seam treatment is a bit easier to do with more structured fabrics that are medium or heavy weight, though some lightweight fabrics are good too. Regular polyester thread works well, but consider using a heavier weight thread such as Button Twist (or doubling the tread feed) for a distinctive top stitch. The texture created by a heavier thread will stand out. You could even pick a contrasting color for an even bolder look. For a stitch that blends in to the fabric, match the regular-weight thread to the fabric. .
For this demonstration I am using a blue cotton shirting without a visibly right and wrong side. I am also using a standard straight stitch presser foot. You can purchase a special "Felling or Lap Seam" foot, but a standard foot works just fine. You could also use an edge stitch foot or zipper foot which can keep your stitching very straight when top stitching. I am using a regular weight polyester thread in white for each stitching line.
Note: Keep in mind that in this demonstration the right side has one line of visible stitching and the wrong side has two lines of stitching
To create flat-felled seams.
Pin and stitch on the seamline, right sides together, like you normally would. I am using Folkwear's standard 1/2" (13mm) seam allowance. Use the seam allowance specified for the pattern you are using.
Trim one edge of the seam allowance to ¼”(6mm) or by at least half of the width of the seam allowance. I have trimmed to approximately 3/8" (10mm) due to the weight of the fabric.
Turn the wider raw edge of the seam allowance under and press it over the trimmed edge, matching the raw edge to the first stitch line.
With the wrong side facing up, stitch close to the turned edge, keeping the stitching straight and even.
The regular straight stitching seen on the wrong side of the garment.