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Understanding Understitching to Create a Sharp, Seamed Edge

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If you are new to sewing, some of the terminology can be confusing. Doesn't "bolt" mean to run away? Cutting something on the "bias" just sounds offensive. And, "feed dogs" seems more like a command than a sewing machine part. Trying to understand exactly what the various terms mean, how they work, and especially when to use them may seem daunting. But, as you learn each one, they'll become commonplace, and soon "nap" will mean more than dropping off for a little snooze. Today, we meet: understitching, which is not a seam done in a sneaky or under-handed manner and/or by Underdog. Read on to find out what it really is.

By definition, understitching is a line of straight stitching sewn just beyond the seam line of two pieces that have been sewn together to create a seam along an edge. One of the pieces is the outside of your project, the other is the inside. In order to keep that seamed edge sharp and clean, you understitch the inside piece to the seam allowance so it won't roll to the outside along the edge seam and look all messy and unprofessional.

Understitching is referred to a lot in garment construction, especially around necklines and armholes with facings. For example, when a facing is sewn to the edge of a scooped neckline, you don't want to see the facing rolling out around the neckline when you wear the garment. You understitch the facing to the seam allowance so the facing stays in place. You might also see understitching around the waist of a lined skirt – the style without a waistband.

Although possibly more common in garments, we've found plenty of uses for understitching in home décor sewing. For example, on our Pleated Crib Skirt (shown below) and our Tiger Eye Box Pleat Pillows (shown above), understitching helps keep the pleats razor sharp along their edges.

Next time you're out shopping for ready made items (a rare excursion for you since finding Sew4home, right?!), look at the inside to see how things are made. You'll notice how often understitching is used to create a professional finish.

How to Understitch

  1. As with the majority of our technique tutorials, we've used unusual fabric and thread combinations so you can clearly see how to execute this technique successfully. In this sample, we selected a light fabric for the inside and a dark fabric for the outside with a bright thread. In your projects, you would use the fabric of your choice (which may or may not be the same for the inside and outside pieces) and thread to coordinate with your selected fabric(s).
  2. If you're sewing a project with instructions provided, such as an off-the-rack pattern or following a downloaded tutorial, there are likely to be references to understitching where appropriate. If you're creating an original, you'll begin to quickly spot where you need to understitch because you'll get that "inside-rolling-to-the-outside" thing happening along a seamed edge. In our example, we will refer to the "inside" as a lining and the "outside" as the right side.
  3. Set up your sewing machine for regular sewing with a straight stitch.
  4. With right sides together and using the appropriate seam allowance, sew the right side piece to the lining piece. Remember, the dark fabric is our outside fabric and the light fabric is our lining.
  5. Grade the seam allowance to eliminate excess bulk in the seam. This means you trim one seam allowance edge narrower than the other.
    Click to Enlarge
  6. Press the graded seam allowance toward the lining.
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  7. Lay the sewn piece flat, right side up. The lining piece should be to the right and the right side piece to the left. The seam allowance should also be laying to the right underneath the lining... since you just pressed it that way.
  8. Place this flat piece under the machine's presser foot. The seam line should be just to the left of the needle, approximately ⅛". You are preparing to stitch on the lining side.
    NOTE: We're using an open toe foot so you can see exactly where to stitch. You would use a standard presser foot on your machine.
    Click to Enlarge
  9. Sew a straight line of stitching through the lining and the seam allowance underneath. This line of stitching should be as long as the edge seam you want to keep from rolling.
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  10. Fold the two pieces back together along seam line (ie. wrong sides together) and press for a sharp edge. Here it is from the back.
    Click to Enlarge
  11. From the front, your seam edge should look straight and clean, just like the photo below. Can't see the lining, can you?
    Click to Enlarge
  12. In case you're wondering what our sewn piece would look like without the necessary understitching... here's a second sample we made. It is identical is all ways except for the understitching. And there's that lining, rolling into view where we don't want it. 
    Click to Enlarge

Contributors

Sample Creation and Instructional Outline: Jodi Kelly

Section: 

Comments (4)

maryhutto said:
maryhutto's picture

I am so glad to see this article! Understitching is one of those extra steps that separates "handmade' from "homemade". In this age of speed sewing and simplified patterns in order to attract more newbies to this art form, it refreshing to read an article on a technique that elevates the average project. The results are so worthwhile!

I love your sight's approach to sewing for the home. You turn utility items into works of art due to your attention to details.Keep up the good work!

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@maryhutto - Thank you so much! You are right, taking the extra time to add those finishing steps makes all the difference - and is often easier than you'd think.

wekebu said:
wekebu's picture

Whoa!  Thank you.  I enjoy creating my own projects, so never knew about understitching.  I usually do a topstitch to hold a seam flat.  You are so right, it does look very professional.

Isn't silk dupioni the most beautiful fabric?

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@wekebu - You are so welcome! And yes, silk dupioni is so lovely!