French seams are double sewn and enclose the raw edges of the fabric in a strong and durable seam that will extend the life of your garment. French seams are best used with very lightweight fabrics and are often recommended for lightweight silk, voile or challis. This seam finish can also be used for lightweight linens and other lightweight fabrics that tend to fray or with sheer fabrics where you don’t want to see a serged or zigzagged finish from the outside of the garment