Here are instructions for several methods of finishing exposed seam allowances that we use at Fit for Art Patterns. Finishing the seams improves their appearance and also protects them from wear or fraying. These techniques can be used in an unlined jacket or pants and for a quilted jacket.
Serged or Zigzag Edges
The simplest seam finish is the serged seam or, if you do not have a serger, a zigzag stitch. Either finish will prevent the fabric in the seam from unraveling and will provide a neat appearance. These machine finishes can be used on each side of the seam allowance if the seam is pressed open, or can finish both seam allowances together if they are pressed to one side.
Set your sewing machine to a zigzag setting wide enough and long enough to capture at least 3 or 4 threads of the fabric in the stitching. Stitch as close to the edge as you can.
A three thread overlock stitch is plenty of thread for finishing your edge with a serger.
A French seam is a narrow seam encased in a slightly wider seam. French seams work best on medium to light weight fabrics and sheers and are particularly good for fabrics that fray easily. Heavy weight fabrics are very bulky in French seams.
Begin by pinning the seam with wrong sides together. It will look like you are sewing the seam on the outside of the garment. Sew the seam at ¼” and press the seam flat. Trim the seam allowance down to 1/8”. Turn the garment and pin the seam again, right sides together, encasing the original seam. Stitch at 3/8” on the wrong side of the fabric and press to one side.
Hong Kong Finished Seams
A Hong Kong finish is a lovely and sturdy finish for seams for medium to heavy weight fabrics. The seam allowances must be at least 5/8” wide and be pressed open.
Cut bias binding strips at least 1” wide from lining, light weight cotton or silky fabric. You will need enough bias strips to finish both edges of each seam.
Place one raw edge of the bias strip against the raw edge of the seam allowance, right sides together. Stitch a ¼” seam connecting the binding strip to the edge of the seam allowance. Press the binding strip away from the seam allowance, then wrap it around the seam allowance and press in to place. The raw edge of the bias strip should be hiding between the seam allowance and the inside of the jacket. Stitch in the ditch next to the bias edge to anchor the raw edge of the bias strip under the seam allowance.
Bound seam finishes completely encase the seam allowance and are excellent for seams that are pressed to one side. For heavy fabrics choose a lining or other light silky fabric to bind your seams. For medium weight fabrics use cotton or silky fabrics. Cut bias strips that are at least 1 3/4”wide and long enough to bind the entire seam.
After you have sewn the seam, trim or grade it to the desired finished width. Pin the binding strip to the seam on the inside of the garment. The edge of the binding strip should extend ¼” into the seam allowance. Stitch along the seam line capturing the binding strip into the seam as you stitch. Press the binding toward the seam allowance.
Press the remaining raw edge of the binding under ¼”. Wrap the pressed edge of the binding strip to the other side of the seam allowance and hand or machine stitch the binding into place, catching the turned edge. If you are making a reversible jacket or want a very flat seam, hand or machine stitch the loose edge of the bound seam allowance to the jacket.