Flat-fell (or felled) seams are one of the workhorses of the fashion world. They are strong, yet attractive and work well for a variety of applications. Most people think of denim jeans when they think of flat-fell seams but this tidy seam-and-finish in one also lends itself well to other projects. I use it on silks, especially on home dec projects or casual jackets that will not be lined.
Traditionally, flat-fell seams are made using a flat-fell foot and one of the seam allowances is trimmed away. I will show you how to make a flat-fell seam using standard presser feet and an untrimmed 5/8" seam allowance. This simple technique has been taught and demonstrated by many sewing experts including Margaret Islander and Claire Schaeffer.
Press a 1/2" fold along seam allowance from right side towards wrong side (the folded edge will become the edge of the seam).
Insert second seam allowance into fold, butting up against folded edge, wrong sides together.
Stitch 3/8" away from folded edge. An adjustable edge guide foot works really well for this. Note: do not worry if you miss any of the raw edge of the folded seam allowance. What matters is that your stitching remains consistently 3/8" from the folded edge.
Lay item flat on ironing board, right sides up, turn and press seam so that underside/raw edges are concealed.
Edgestitch along folded edge. I like to use the blind hem or edgestitch feet for this.
That's it! No trimming necessary! Wasn't that easy? If you are working on a curve, you may need to clip the folded seam allowance. Be sure not to clip through the folded edge.
Here's what the finished seam looks like:
Of course, you can choose to construct the seam with either side to the front - it's up to you!