25 Feb 2020 • • by Heather Lou

The Hows and Whys of Underlining Fabric Explained


In our post on sewing a proper muslin, I mentioned underlining a few times and want to revisit the subject today. Underlining fabric is often a misunderstood concept, so I'd like to explain exactly what underlining is and what it does for your sewing projects (spoiler alert: a LOT).

Sewing jargon can be confusing, so it's not unusual to be mystified about the difference between lining, underlining and interlining. A traditional lining is likely something you've sewn before. It is a layer between the main fabric and your skin that hides construction, creates a smooth surface to skim over your body, and is attached around necklines and sleeves to create a completely clean finish from the inside. Most of the time it hangs free at the hem.

Underlining, on the other hand, is a layer of fabric that is basted to your fashion fabric so that both layers act as one. It doesn't hide or encase anything, so you still have raw seams that need to be finished in one way or another. An underlining doesn't replace a lining, and in most applications, you would need to still add a lining to create a clean finish. An interlining is similar to an underlining, but it's done primarily to add warmth (we have a full tutorial on interlining for warmth here).


There are SO many ways underlining will help elevate your sewing projects! Let this list convince you:

  • Helps add body and stability to loosely woven fabrics, and adds structure to fabrics that may be too drapey or light-weight for the necessary application
  • Helps make transparent fabrics opaque or shift the colour of the fashion fabric depending on the colour of the underlining fabric
  • Helps hide seam "show through" of seam allowances, seam lines and other construction details
  • Acts as a base for all construction marks so you don't need to mark your fashion fabric
  • Creates a solid base to stabilize details like welt pockets and other design features
  • Provides a layer to secure hand stitching to so these stitches are invisible from the right side of the garment (ie. catch stitching seam allowances in place)
  • Minimizes wrinkling since the fabric is bulked up
  • Can add warmth to garments by introducing a second layer
  • Adds strength and durability to garments and fabric, increasing the lifespan of your me-mades


Many different types of fabrics can be used to underline; what you choose depends on the application. In general, you want something a bit lighter than your fabric, and you need to make sure the colour works with or doesn't show through your fashion fabric. Here are the most common types:

  • Silk Organza - silk organza is a miracle fabric and works extremely well as an underlining. Silk organza is lightweight, translucent and has a crisp but flexible hand, making it a great choice to add body to fabric. The crispness still has some fluidity to it so it will mold to the fabric and your body. Polyester organza should never be substituted since it doesn't have the breathability and flexibility and doesn't press as well, and you should also be mindful of quality, since some silk organzas are slippery and less stable. The best quality I've found can be found in Susan Khalje's shop. I suggest always having a few yards in your stash since there are so many ways you can use it (use the selvage to stabilize a neckline, as sew-in interfacing, to stabilize design details, or to use as a press cloth).
  • Flannel - soft and cozy, flannel is a great choice to add warmth to a garment or add a soft layer to your fashion fabric (great for drapey fabrics like silk)
  • Cotton batiste - lightweight, soft and semi-sheer, batiste is a great basic choice for most underlining applications
  • Cotton broadcloth or muslin - a bit stiffer than batiste, this is best when you need a more structured shape like in a jacket, or need to hide inner construction details like boning. If you used an appropriately weighted muslin fabric for your toile, you can actually use that muslin as your underlining, although you can obviously only do this if you don't plan on making the garment again.
  • Crepe de chine - helps beef up sheer, lightweight or drapey fabrics

When trying to decide what type of fabric to use as your underlining, cut out scraps of your fashion fabric and underlining and layer them together. How does it drape together? Can you see the underlining through the fabric? Does it have the structure and stability you're looking for? Testing a few different options will help you understand what your fabric and garment needs.


At its simplest, an underlining is essentially a double of your fashion fabric. If you're not sewing a couture garment, you can simply use your pattern pieces to cut out your fabric and underlining separately, with any construction marks transferred to the underlining only. Once cut, you'll then machine baste the layers together using a long stitch line just inside the seam allowance (this gets removed later). For basting, I highly recommend a walking foot since it will ensure the layers don't shift while sewing. To be extra accurate I also suggest hand basting along the length of the piece's grainline first, which can be removed later. You'll also want to note any hem allowances and trim the underlining at that point since you don't want the underlining to extend into the hem seam allowance. Give the pieces a good press and make sure both layers are laying flat against each other without any puckering or bubbling - if you see that you'll have to restitch the area.

Once your pieces are secured with basting, you can now proceed to sew your garment as usual; now with your beefier, and happily underlined pieces!


In a couture application, underlinings are almost always used. Since couture garments involve a lot of hand stitching (catch-stitching seam allowances, hand stitching in linings, etc) the underlining is the layer that holds those stitches so you can't see them. It also acts as the pattern or template when you're cutting out your fabric. As I mentioned in our last post on sewing muslins, in a couture project the muslin is often used as a basic pattern. Using transfer paper and a tracing wheel, all stitching lines and construction marks are then transferred from the muslin to the underlining, which is then cut out and used to cut out the fashion fabric. Silk organza is GREAT for this since it's transparent, making it really easy to see your fabric beneath, and by marking it instead of the fabric, you prevent overhandling of your fashion fabric.

Once you've completed your muslin and are ready to move on to cutting your fabric, the first step is to use transfer paper and your wheel to transfer all your marks and seam lines to your underlining. To start, securely pin the muslin to the underlining (in the photo below I've used silk organza). Pin frequently around the perimeter and also strategically through the middle of the piece so the two layers are stable. Once that's done, place the underlining on top of transfer paper (coloured side up) and use your tracing wheel to transfer all your construction lines.

You can now use the underlining as your pattern piece. Below you can see my silk organza layered over my fashion fabric - I've cut extra-large seam allowances I'll trim down later (this is one of the secrets of couture - a lot of it is rough! Cutting is actually pretty fast since you're not fussing around trying to be exact when cutting out seam allowances). Keep in mind you can use any type of underlining fabric for this step - since your grainlines are clearly marked, you'll use those to find grainline on the fashion fabric even if you can't see through it like you can with the organza.

Again, the interlining is securely pinned to the fabric before the fabric is cut out. If you were sewing a non-couture project, at this stage you would machine baste the layers together around the seam allowance, but because it's couture, the process is a bit longer.


Hand basting is a key step in any couture project. Since couture is all about control (control freaks and Virgos rejoice!), machine basting isn't a good option since there are too many ways the fabric can shift and distort. Instead, you want to use a smooth basting thread to secure the layers together by hand. You can use silk thread, but I've tried a few things and this style of Japanese basting thread is the best. It doesn't snag, runs smoothly through layers and is thick enough to easily see on your pattern pieces. You'll want to use a longer needle like these ones since it makes it easier to pick up multiple stitches at a time. Since you may have to do a lot of needle threading, I suggest picking up one of these cute needle threaders to save yourself some squinting and poking.

Once your underlining is pinned in place, it's time to thread up that needle and start hand basting along your stitch lines. Yes, every single stitch line. It goes faster than you think since you're using nice long stitches, and by working at a flat table (very crucial to avoid distorting your fabric) you can pick up a few stitches at a time and make fairly short work of it. Susan recommends sewing right on top of the stitch line, but since you'll eventually be stitching on top of your hand basting with machine stitches, you end up spending a ton of time meticulously removing the basting thread with a seam ripper. Personally, I prefer sewing just inside the stitch line (less than a millimetre) to  make it easier to remove. In the example below, I basted right on the stitch line and spent hours removing the basting thread before I changed my strategy.

What all this thread basting does is securely anchor your layers together everywhere it counts, making it really easy to assemble the garment with minimal distortion.

I'm currently working on another couture-ish project and I used thread basting to secure the fabric, batting and lining together for this quilted jacket. I did it really quickly and roughly since I'm planning on machine quilting all these layers together, but you can see how big my stitches are. This took less than ten minutes to do.

As with most sewing techniques, there is generally a "fast" and "couture" option. Whether you'll want to machine baste or hand baste your underlining is up to you, but these days I pretty much always resort to hand basting since it gives me the thing I want most in life: control. Regardless of whether you're down to spend some time with your hand sewing needles, I hope this post helped demystify underlining for you, and encourage you to try this technique the next time you need to add some body, stability or warmth to your sewing projects.

Have you experimented with underlining? How did it go?

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