French seam is suitable for thin and sheer fabrics. Don’t come apart. But unsuitable for heavyweight fabrics.
Making of French seam
Lay 2 fabrics with right side out, and sew the 3mm line from the edge.
Press the seam allowance towards the one side,…
and fold the fabric with right side together.
Then sew the finishing line.
Press the seam allowance towards the one side, It’s done.
French seam movie is the following.