Bound Seams: What, When, and How

Sewing a bias bound seam is a technique for finishing seams neatly. It encases the raw edges completely, prevents fraying and gives any project a professional look. The seams are cleanly finished on both sides. In this blog I will explain how a bias bound seam is different from other types of seams like a french seam or a flat felled seam. I will go over the different uses of the bound seam, show you how to sew the bound seam correctly and give you some extra tips.

A bound seam is a type of seam where the cut edges of the project’s seam are enclosed with bias tape to keep them from fraying. You can bind the seam allowances of both fabrics with one piece of bias tape or enclose the two separately, like shown here and explained below.

Bound seams are particularly useful for unlined garments or accessories like jackets or pouches, as it encases the raw edges. This type of seam is great when you can afford a little bit of extra bulk, when you are pressing the seams open and when you know both sides of the seam will be visible. A bound seam finish could be used for purely aesthetic reasons but can also be a matter of necessity. It can be a great solution when a seam allowance is so loosely woven that zigzag or serger stitches pull right off the edge. By choosing a contrasting color of bias tape, you can add interesting colors to the inside of your project and uplift your project.

On bags and purses and sometimes children’s or women’s clothing bias bound seams are also used on the outside of the project. Bias tape is perfect to be used on curved seams because it doesn’t pucker. In these cases both seam allowances are bound together in one bias tape strip.

If you look for this type of seam, you will come across a Hong Kong Seam. The Hong Kong seam is similar to the Bias Bound Seam. These seams both use a binding strip to hide the raw edges. The difference between a bound and Hong Kong seam finish is that the edges of the binding strip used are turned under both the front and the back; the underside strip edges of a Hong Kong finish are left raw to reduce bulk. Both seam techniques require two lines of stitching to complete. From the top both seams look the same.

• bias tape (store-bought or homemade)
• a sewing machine with needle and matching thread
• pins or clips
• an iron and ironing board
• optional: bias tape maker
• optional: stitch-in-the-ditch presser foot

• Width: use 1 inch cut binding, this is ½ inch single fold, and ¼ inch double fold bias binding. The ideal width for bias tape for bound seams also depends on the weight and stability of the binding fabric, and the thickness of the project’s fabric. If you are making bias tape yourself, you can test out several widths before deciding on one - a few millimeters in width can make all the difference between an agreeable or exasperating - sewing process.
• Select a thin, lightweight fabric. Tightly-woven natural fabrics such as silk or 100% cotton work well. If the seam is inside a skirt or a lined jacket, choose a color that blends with the fashion fabric. For unlined jackets, where the seam finish will show, choose a contrasting color and/or print just for fun, but make sure it won't shadow through to the garment’s right side. For a luxurious finish you can use glossy silky bias tape. Note that thin slippery fabrics are not easy materials to work with.

To sew a bias bound seam follow these seven steps:

1. Prepare the Fabric and Sew a Regular Seam:

• • Lay your fabric pieces right sides together, aligning the edges and pin in place, like you would normally do to sew a regular seam.
  • Sew this seam with a ⅜” to a ⅝” seam allowance. You can use different seam allowance sizes but you will have to change the size of bias tape that you will be using. A wider bias tape asks for a wider seam allowance. If you use a wide seam allowance and a narrow bias tape, the bound edge will be further from the stitching. To play it safe, you can always start with a wider seam and trim it before you apply the bias tape. With a very narrow seam allowance it is more difficult to attach the bias tape neatly.
  • Use a straight stitch.

• • Press the seam open to make the seam lie flat. This will make it easier to apply the bias tape.

2. Prepare the Bias Tape:

• • Cut the bias tape the length of the seams you will be sewing. You need two pieces of bias tape for one seam.

You can make your own bias tape easily with a bias tape maker. We have a complete bias making tool set on MadamSew.com. Check out our bias tool set video if you are interested.

Bias tape is best cut on the bias, this is at a 45-degree angle to the fabric grain, which gives it stretch and flexibility. Cut strips of fabric of 1 inch on the bias. Grab the (yellow) bias tape maker, size ½ inch (single fold), pull the strip through and iron the folds flat. The raw edges are now pressed to the center. Then fold the bias taps in half lengthwise with the pressed raw edges facing each other and press the extra fold in the center.

3. Attach the Bias Tape:

• • Open up one folded edge of the bias tape.
  • Align a raw edge of the bias tape with the raw edge of the wrong side of the seam, right sides of the seam allowance and bias tape facing each other.
  • Pin or clip the bias tape in place along the seam allowance

• • Sew along the first fold line of the bias tape closest to the raw edge with a ¼” seam allowance. This will be just inside the first crease line on the bias tape.

• • Turn the bias binding to the right side and press seam allowance towards the bias binding.

4. Wrap the Bias Tape Around the Raw Edge:

• • Fold the bias tape over the raw edge, encasing it completely. The center crease of the tape is hugging the raw seam edge. The seam allowance should fill the binding. It can be trimmed a bit, if required. If the seam allowance doesn’t fill the bias tape binding, stick to the original fold of the binding.
  • Tuck the remaining folded edge of the bias tape under, aligning it with the seam stitching line. This folded edge should overlap the first stitching line by 1/16” to ⅛” (1-2 mm).
  • Press and pin or clip in place. When pinning, be sure to check that you are catching the folded edge of the binding on the back.

5. Topstitching

• • Carefully stitch the binding to secure it in place by topstitching on the binding that you just folded and pinned in place. Stitch about 1/16” from the ditch, as close as possible, on the bindings edge. Use a thread that matches your binding.

6. Repeat for the Other Seam Allowance:

• • Repeat steps 3–5 on the other seam allowance.

7. Final Pressing:

• • Once both seam allowances are bound, give the entire seam a final press with your iron to set the stitches and ensure a smooth, professional finish.

Now, your bias bound seam is complete! The raw edges are neatly encased, giving your garment or project a clean and durable finish.

1. Practice Makes Perfect

Trying this technique out ahead of making your final project will definitely be helpful. So grab some scrap fabric and do a test run.

2. How to Tame Slippery or Unstable Fabrics

When you use these to make bias tape, press them with some spray starch before cutting.

Bias strips are naturally stretchy; and cutting them from a slippery fabric only increases the likelihood that the bias will stretch more than the project’s fabric as you sew. If the bias strip begins to bubble in front of the presser foot, sink the needle, raise the presser foot, and gently ease the strip toward the needle. Reset the presser foot and continue sewing. You can also use a walking foot to make both the fabric and the bias tape move consistently under the sewing machine.

3. Check the underside regularly when sewing.

To avoid unpicking a part of your sewn bias tape, check the underside of the seam allowance regularly when stitching on your machine. The other seam allowance can easily be caught while sewing.

4. Narrow topstitching

When topstitching the bias tape, you have to sew close to the folded edge. This can be tricky. As a tool tip, you could use the edge joining foot. This foot has a guide that helps you stitch close to the edge consistently.

Using bound seams on your project isn’t the fastest way to finish edges on a sewing project but it truly is a neat looking finish and an alternative to using lining on some garments. Adding lining to a jacket definitely takes more time than adding bias tape to the seams.

Hope you learned something new and are trying this type of seam on a future project.

We also have a tutorial on how to sew two other types of seams:

• A French Seam
• A Flat Felled Seam

Don’t hesitate to send me an email if you have any questions, an@madamsew.com.

Happy Sewing!

An

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