Understitching vs Topstitching: What’s the Difference & Why It Matters

Have you ever finished a waistband or facing, pressed it carefully, and then—seconds later—it flips right back out? It’s one of the most frustrating sewing problems, and it can make even beautifully sewn garments look a little “off.”

The solution is a simple step called understitching. It doesn’t take long, but it makes a world of difference in how your clothes look and feel. In this post, I’ll explain what understitching is, why it’s worth doing, and how it differs from topstitching. By the end, you’ll know exactly when to use each technique.

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What is Understitching?

Understitching is a line of stitching that secures the seam allowance to the inside of your garment—usually to a facing, lining, or waistband. You sew very close to the seam line, on the inside layer only, so from the outside, it’s invisible.

Think of it as a way of “training” your fabric. By anchoring the seam allowance in place, understitching encourages the inside of your garment to roll inwards neatly and stay put.

You’ll often see understitching used on:

• Waistbands

• Neck facings

• Armhole facings

• Linings in skirts, dresses, and trousers

It’s one of those details that professional garments often include, but many home sewists skip—either because they don’t know about it or think it isn’t worth the time.

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Why Should You Understitch?

If you’ve ever had a waistband that insists on rolling out, you’ll already understand the value of understitching! Here’s why it matters:

✨ Prevents rolling – It keeps facings, linings, and waistbands from creeping to the outside.

✨ Creates a flatter finish – Your seams lie beautifully smooth instead of puffing or twisting.

✨ Looks more professional – Even though you don’t see it, the effect shows in the overall polish of the garment.

✨ Improves comfort – A flat, secure facing or waistband feels better against your body.

It’s a small step that takes just a minute or two, but the difference in finish is huge.

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Understitching vs Topstitching

Here’s where people get confused: isn’t topstitching doing the same thing? Not quite. Let’s break it down.

Topstitching:

• Always visible on the outside of the garment

• Can be decorative and functional

• Adds durability and design detail

• Examples: jeans seams, pockets, hems

Understitching:

• Hidden on the inside of the garment

• Purely functional—it’s there to hold layers in place

• Not decorative, but essential for neatness

• Examples: waistbands, facings, linings

So while topstitching makes a statement on the outside, understitching quietly does the behind-the-scenes work. Both have their place, but they achieve very different results.

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When to Use Each

• Use understitching when you want the outside of your garment to look clean, flat, and uninterrupted—like waistbands, necklines, and facings.

• Use topstitching when you want visible strength or a design feature—like on denim, casual wear, or where seams need reinforcement.

• Sometimes you’ll even use both in one garment, depending on the look you’re going for.

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Example: Understitching the Emerson Trousers Waistband

In my own sewing, I use understitching regularly. Here’s how it looks on the Emerson trousers waistband:

1. Sew the waistband facing to the trousers as normal.

2. Press the seam allowance up towards the facing.

3. Stitch very close to the seam, catching the facing and seam allowance together.

4. Flip the waistband back into position and give it a good press.

That’s it! The waistband stays neatly to the inside, instead of rolling out. A tiny effort for a huge improvement in finish.

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Final Thoughts

Understitching might feel like an “extra” step, but really, it’s a shortcut to a more professional result. Once you get into the habit of doing it, you’ll wonder how you ever skipped it.

So next time your waistband or facing tries to misbehave, try understitching—you’ll see the difference straight away.

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And if you’d like more bite-sized sewing tips, follow me on Instagram @NeedleSayMore. I share simple, practical techniques that make sewing easier, calmer, and more rewarding.