French seam
Definition
A French seam is an enclosed seam sewn twice, first wrong sides together and then right sides together, so both raw edges are hidden inside a narrow fold.
French seams look as neat inside as outside, with no fraying edge and no need for a serger. They are the standard for sheer and lightweight fabrics such as voile, chiffon, lawn, silk and viscose, for unlined garments, and for bias-cut slip dresses, where an overlocked edge would show through.
With a 1.5 cm (5/8 in) seam allowance:
- Place the pieces wrong sides together and sew at 6 mm (1/4 in) from the edge.
- Trim the allowances to about 3 mm (1/8 in) and press the seam open, then fold the pieces right sides together along the seam and press flat.
- Sew at 9 mm (3/8 in) from the fold, enclosing the raw edges.
- Press the finished seam to one side.
The two seams add up to the original 1.5 cm, so the garment keeps its size. With a 1 cm (3/8 in) allowance, sew at 4 mm and then 6 mm.
Check the right side after the second seam: if whiskers of fabric poke through, trim the first allowance closer next time. French seams suit straight or gently curved seams. On tight curves, such as armholes with a set-in sleeve, and on bulky fabrics, choose another seam finish or a flat-felled seam.