Flat-Felled Seam

Where a French seam hides everything on the inside, a flat-felled seam puts its construction on display: two crisp, parallel rows of topstitching visible from the outside, with the raw edges folded and enclosed flat against the fabric rather than standing up inside a tube. It's the seam on the outside leg of a pair of jeans and down the sides of most work shirts — chosen for durability as much as for looks. Nothing frays, and there's no seam allowance left loose to catch or wear through.

It takes more steps than either a plain seam or a French seam, and it only really works on a seam you can press flat and access from both sides — set-in sleeves are awkward, straight side seams and inseams are exactly what it's built for. I reach for it on anything that's going to get hard wear: workwear, kids' clothes, garments that'll be washed constantly.

How I do it:

1. Stitch the seam right sides together at the full seam allowance, then press both allowances to one side together, as a pair.
2. Trim the underneath allowance down to about 1/8", leaving the top one full width.
3. Fold the wider allowance over the trimmed one, enclosing it, then fold the raw edge under itself once more and press flat against the garment.
4. Topstitch close to that folded edge, catching all the layers underneath.