Flat felled seams are one of my favourite ways to finish a garment. The raw edges are completely enclosed and the seam allowance is stitched flat so it’s extremely neat, durable, and comfortable to wear. It’s a seam that is most commonly used on garments like denim jeans. You can also make the seam a feature by using thread in a contrasting colour.
Flat felled seams require a 1.5cm seam allowance so you may have to adjust your pattern pieces before cutting. Start by sewing the seam at 1.5cm with either the right or wrong sides of the fabric together, depending on the result you want. If you start with the wrong sides together you’ll end up with 2 rows of stitching on the outside. If you start with the right sides together you’ll just have the 1 topstitching line on the outside.
Next, trim away the seam allowance on the side that you want your stitching lines on. You’ll want to trim it down to about 5mm.
Press the longer seam allowance in half so that it folds over the shorter seam allowance. The raw edge should be just beside the stitching line.
Next, press the seam flat so that all the raw edges are enclosed.
Edge stitch the folded seam allowance in place.
And you’re done! You can now add flat felled seams to your garments for a super sleek and durable finish. Let me know if you have any questions!