The raw edge of the seam allowance is enclosed in a secondary seam.
Light weight fabrics and fabrics that are prone to raveling. Ideal for items that will have visible seams.
Produces a very neat, clean, finish. Raw edges will not ravel because they are completely encased.
Adds bulk to the seam allowance, making it unsuitable for medium to heavy weight fabrics. A little complicated to make. Somewhat time consuming. Requires precise sewing.
How to Make
Assuming your item has a 5/8” seam allowance, place your fabric pieces wrong sides together. Stitch 3/8” from the edge. Trim the seam allowance down to about 1/8”. Press the seam allowance open. Fold the item right sides together at the seam line, then press. Stitch 1/4” from the folded edge. Press the seam allowance to one side.