Underlining and Interlining: Inner Structure for Tailored Garments
Underlining and interlining add weight, opacity, warmth, and structure invisible from outside. Here's the difference between them, when to use each, and how to apply them cleanly.
Underlining and interlining are the invisible layers behind tailored garments. From the outside, you can’t tell they’re there. From the inside (especially after the lining is attached), you still can’t tell. But the garment hangs differently — heavier, more structured, opaque where the fashion fabric would have been transparent, warmer where you needed warmth. These are the layers that turn fashion fabric into a finished tailored piece.
The terms get confused. People call any internal layer a “lining” when it might actually be an underlining or interlining. The distinctions matter because they’re applied differently and serve different purposes.
This guide clarifies the differences, covers when to use each, and walks through the application techniques.
The three “lining” layers — definitions
Three terms that sound similar but mean different things:
Lining
The visible inner fabric layer. Constructed as a separate inner garment that mirrors the outer. Visible when the garment is opened or when you look inside.
Already covered in our linings guide.
Underlining
A fabric layer sewn to the wrong side of the fashion fabric, treated as one piece during construction. The fashion fabric and underlining are bonded (by stitching, not by adhesive) before any other construction.
The underlining is not visible because the fashion fabric is on top, and the lining (if there is one) is below.
Purpose:
- Adds weight or body to lightweight fashion fabric.
- Adds opacity to transparent or thin fashion fabric.
- Adds structure to drapey or unstable fashion fabric.
- Stabilises bias-cut fabric.
Interlining
A fabric layer placed between the lining and the fashion fabric, with both lining and fashion fabric attached separately to it. Common in winter coats for warmth.
The interlining is also not visible because it’s sandwiched between two other layers.
Purpose:
- Adds warmth (insulation).
- Adds extra structure or support.
- Modifies how the layers move together.
When to use underlining
The most common applications:
To add opacity
A lightweight white fabric with a darker garment underneath shows through. An underlining of solid white cotton (cut to match) blocks the show-through.
This is essential for white wedding dresses, formal eveningwear, and any garment where the fashion fabric is too transparent.
To add weight or body
A lightweight silk or chiffon hangs limply on a structured pattern. An underlining of cotton lawn or silk organza adds enough body to support the design.
This is common for tailored skirts in lightweight fabric, where the fabric alone wouldn’t hold the shape.
To stabilise bias-cut fabric
Bias-cut garments stretch and distort over time. Underlining with a stable fabric (cut on grain, not bias) holds the shape.
This is how bias-cut couture dresses keep their shape decades after being made.
To prevent show-through of construction
Pad stitching, dart stitching, and seam allowances can sometimes show through fashion fabric to the right side. An underlining intercepts these and prevents show-through.
This is common in tailored garments with hair canvas — the underlining blocks the canvas from being visible through the wool.
To match colour with a darker pattern
If you’re making a garment with bold colour blocks (one fabric in dark, one in light), the dark fabric showing through to the light side is a problem. Underlining the light side with a matching light fabric solves it.
When to use interlining
For warmth in coats
The classic application. A wool coat with a cotton flannel interlining is significantly warmer than the same coat without. The interlining sits between the wool and the lining, trapping warmth.
For insulation in technical garments
Nylon-coated cotton coats, military-style outerwear, and similar garments may use a synthetic insulation interlining (Thinsulate, fleece) for warmth without bulk.
For specific structural needs
A heavily tailored coat may use an interlining to reinforce specific areas or to hold a particular shape that the fashion fabric alone can’t maintain.
Underlining: how to apply
The technique is straightforward but specific.
Step 1: Cut underlining to match fashion fabric
Cut each underlining piece to the same shape as the corresponding fashion fabric piece. Same darts, same notches, same grainline.
For most underlinings, the underlining is the same size as the fashion fabric. For some specialty underlinings (e.g., silk organza for couture), the underlining is sometimes cut slightly smaller to prevent it from peeking out at edges.
Step 2: Layer the two fabrics
Lay the underlining on the wrong side of the fashion fabric, with edges aligned and grainlines parallel.
Step 3: Baste the layers together
Hand-baste (with long running stitches) along the seam lines and key markings. Don’t fully sew — basting holds the two together temporarily, allowing them to be unbasted if needed.
Some sewers machine-baste with a long stitch instead of hand-basting. Either works.
The two layers are now treated as one for all subsequent construction.
Step 4: Construct the garment normally
Sew darts, princess seams, side seams, and any other construction. The two layers go through together as one. The underlining adds weight, opacity, or structure, and the fashion fabric remains the visible layer.
Step 5: Trim seam allowances
After the garment is constructed, trim the underlining at seam allowances to reduce bulk. Leave the fashion fabric’s seam allowance at the standard width.
Step 6: Press carefully
Underlined fabric requires careful pressing. The two layers can shift if pressed too aggressively.
For pressing technique, see our pressing techniques guide.
Common underlining fabrics
| Underlining | Used for |
|---|---|
| Silk organza | Lightweight underlining for delicate fabric (couture standard) |
| Cotton lawn | Mid-weight underlining for moderately structured garments |
| Cotton voile | Lightweight underlining for thin fabric |
| Muslin | Cheap underlining for muslin-fitting projects |
| Bemberg / Cupro | Slippery underlining that doubles as light lining |
| Hair canvas | Tailoring underlining for jackets and coats |
| Fusible interfacing | Quick alternative — less drape but faster application |
The right underlining depends on what you’re trying to achieve. For opacity, use a fabric matching the fashion fabric’s colour. For body, use a fabric of medium weight. For couture-quality drape, use silk organza.
Interlining: how to apply
Slightly more complex because three layers are involved.
Step 1: Cut interlining to match the lining
The interlining is typically cut to the same dimensions as the lining (slightly smaller than the fashion fabric, in some cases).
Step 2: Layer interlining and lining
Place the interlining on the wrong side of the lining (with edges aligned). Baste together at seam lines.
Step 3: Construct the lining as normal
The interlining and lining are now treated as one piece for all lining construction. Sew lining seams, darts, etc. through both layers.
Step 4: Attach the lined-and-interlined inner to the fashion fabric outer
The standard lining attachment process applies. Bag out the lining as you would normally — the interlining is sandwiched between the lining and outer.
Step 5: Trim and finish
After the garment is bagged out, trim the interlining at seams to reduce bulk if needed. The interlining is hidden between the lining and outer.
Common interlining fabrics
| Interlining | Used for |
|---|---|
| Cotton flannel | Lightweight warmth in coats and jackets |
| Wool batting (felt-like) | Heavier warmth in winter coats |
| Thinsulate / synthetic insulation | Modern lightweight warmth |
| Fleece (lightweight) | Casual warmth, less formal |
| Hair canvas | Structural interlining (less common; usually used as underlining instead) |
Underlining vs interlining: practical examples
To clarify the distinction:
Example 1: Lightweight white linen blouse
You’re making a fitted blouse in lightweight white linen. The fabric is somewhat transparent and lacks body for the structured cut.
Underline with white cotton lawn. The two layers are sewn together as one. The garment now has the right opacity and body.
No interlining or lining needed for a casual blouse.
Example 2: Wool winter coat
You’re making a tailored wool coat for cold weather. The wool itself doesn’t add enough warmth.
Apply hair canvas to the front of the coat as an underlining (pad-stitched).
Apply cotton flannel as interlining between the lining and the fashion fabric for warmth.
Apply Bemberg as full lining for the slippery interior finish.
The coat has four layers: fashion fabric (wool), underlining (canvas), interlining (flannel), lining (Bemberg). All four serve different purposes.
Example 3: Bias-cut silk dress
You’re making a bias-cut silk slip dress. The bias is naturally drapey but unstable over time.
Underline with silk organza (also bias-cut, but the bias-on-bias double layer is much more stable than single bias).
No interlining needed.
Optional lining for slipping on smoothly. Or no lining if the garment is self-finished.
Common underlining/interlining mistakes
Skipped pre-treatment of the underlining
Underlinings shrink. If the underlining wasn’t pre-shrunk, it’ll shrink on first wash and pull the fashion fabric out of shape.
Used the wrong weight
Underlining with too-heavy fabric adds bulk. Underlining with too-light fabric doesn’t add the weight you need. Match the underlining to the project’s specific needs.
Underlining shows at edges
Underlining cut too large extends past the fashion fabric’s edges, becoming visible. Cut underlining slightly smaller (about 5 mm) than the fashion fabric.
Interlining adds too much bulk
Heavy interlining can make the garment stiff or bulky. Test on a sample before committing to a heavy interlining for the whole garment.
Pad stitching shows through
If pad stitching is going through both fashion fabric and underlining, sometimes the pad stitches show on the fashion fabric. The fix: pad-stitch only through the underlining (not the fashion fabric), then attach the fashion fabric on top with a separate basting.
When to use each: the cheat sheet
| Need | Solution |
|---|---|
| Add opacity | Underlining |
| Add body to lightweight fabric | Underlining |
| Stabilise bias fabric | Underlining |
| Hide construction details | Underlining |
| Add warmth | Interlining |
| Add insulation | Interlining |
| Finish the inside cleanly | Lining (covered in our linings guide) |
Most tailored garments use multiple layers — fashion fabric, underlining, sometimes interlining, lining.
Tools and supplies
- The fashion fabric (already cut).
- Underlining or interlining fabric (cut to match).
- Hand-sewing needle.
- Long basting stitches (run with cotton thread).
- Iron and ironing board.
- Pins.
Closing thought
Underlining and interlining are the invisible layers that distinguish tailored garments. They’re not visible in the finished garment, but their effect on the way the garment hangs, drapes, and holds shape is significant. A skirt with proper underlining drapes differently from the same skirt without; a coat with proper interlining is dramatically warmer.
Most beginner sewing skips these layers. Most tailored sewing depends on them. The transition from intermediate to advanced sewing is partly about adding these invisible layers to your construction toolkit.
For the broader advanced techniques that build on underlining knowledge, see our complete advanced tailoring roadmap. For the visible inner layer (the lining), see our linings guide.