Interlining is a hidden layer of fabric sandwiched between the outer material of a garment (or curtain) and its lining. Its job is to add structure, shape, reinforcement, or warmth to the finished product. You never see it in the completed piece, but it’s the reason a suit collar stays crisp, a coat keeps you warm, and a waistband doesn’t flop over after a few wears.
How Interlining Differs From Lining and Interfacing
These three terms get mixed up constantly, but they serve different purposes and sit in different places within a garment. A lining is the innermost layer you can see and touch when you flip a jacket inside out. It protects the outer fabric from body oils and sweat, reduces friction so the garment slides on easily, and helps the fabric hang properly. Interlining and interfacing, by contrast, are both invisible in the finished piece, tucked between the outer fabric and the lining.
Interfacing is applied to specific parts of a garment: collars, cuffs, waistbands, plackets, and button bands. It controls stretch and adds localized stiffness. Interlining can serve a similar structural role, but the term also covers full layers added for warmth, as in a quilted winter coat. In everyday sewing conversation, “interfacing” and “interlining” often overlap, and many sewers use them interchangeably when talking about structural reinforcement. The key distinction is that interlining can span an entire garment panel for insulation, while interfacing targets only the spots that need extra body.
What Interlining Actually Does
Interlining performs four main jobs depending on where and why it’s used:
- Shape and stiffness. Collars, lapels, and cuffs hold their form because of the interlining behind them. A well-reinforced shirt collar keeps its crisp shape through dozens of wash and ironing cycles.
- Shape retention over time. Without interlining, fabrics in high-stress areas sag, stretch, or wrinkle permanently. Interlining prevents that distortion.
- Reinforcement. Lightweight or loosely woven fabrics tear more easily at stress points like buttonholes and pocket openings. Interlining strengthens those zones.
- Thermal insulation. In coats, jackets, and even curtains, a full panel of interlining traps air between layers, adding warmth and body.
Fusible vs. Sew-In Interlining
The two main categories are defined by how they attach to the outer fabric.
Fusible interlining has a heat-activated adhesive coating on one side. You press it onto the fabric with an iron (or an industrial fusing press), the adhesive melts and bonds permanently, and no stitching is needed. It produces a crisp, structured finish and works well for tailored garments like blazers, jackets, and dress shirts. In industrial settings, the adhesive melts at temperatures between about 130°C and 160°C (roughly 265–320°F), and performance is best within about 7°C of the target temperature. At home, your iron’s “wool” or “cotton” setting generally lands in the right range.
Sew-in interlining is basted or stitched to the fashion fabric by hand or machine. It creates a softer, more flexible hold and preserves the natural drape of the outer material. Because there’s no heat involved, it’s the safe choice for delicate or heat-sensitive fabrics like silk, velvet, and beaded textiles. Couture and handmade garments often use sew-in interlining for the precise control it offers.
A quick way to decide: if you want structure and speed, go fusible. If you want drape and softness, or your fabric can’t take heat, go sew-in.
Common Materials and Structures
Interlining comes in three structural types, each suited to different fabrics and projects.
Woven interlining is constructed like regular fabric, with threads running lengthwise and crosswise. It has a grainline you need to align with your pattern pieces, just as you would with your fashion fabric. It pairs well with medium to heavyweight wovens and with delicate fabrics like silk that need body without bulk.
Knit interlining has crosswise stretch and minimal lengthwise stretch, so it moves with the fabric rather than fighting it. It’s the go-to for knit garments, but it also works well with lightweight wovens that have natural drape, like rayon or challis.
Non-woven interlining is made from fibers bonded together by heat, chemicals, or pressure rather than woven or knitted. It’s the most common type in ready-to-wear clothing because it’s inexpensive and easy to produce. It has no grainline, so you can cut it in any direction, though it tends to offer less drape than woven or knit options. The fibers are typically polyester, nylon, viscose, or cotton, often blended for specific performance characteristics.
Choosing the Right Weight
The most reliable guideline is to pick an interlining that’s the same weight or lighter than your outer fabric, with slightly less drape. This adds structure without making the reinforced area feel stiff or out of place compared to the rest of the garment. A lightweight cotton shirt, for instance, calls for lightweight, flexible interlining. If you used something too heavy, the collar and cuffs would look rigid and unnatural against the soft body of the shirt.
For structured outerwear, you can move up to a medium-weight interlining to get more body, but still stay at or below the weight of the outer fabric. Even projects that seem like they’d need heavy reinforcement often don’t. A floppy sun hat, for example, needs only lightweight interlining in the brim to give it gentle structure while still letting it drape. Going heavier would turn it into a stiff visor.
Interlining in Home Textiles
Interlining isn’t limited to clothing. In curtain making, it’s an extra layer placed between the decorative face fabric and the standard curtain lining. This sandwich of fabric traps air, improving thermal insulation, which is especially useful for large windows or drafty rooms. It also gives curtains a noticeably fuller, heavier hang that looks more luxurious than an unlined or single-lined panel. The same principle applies in some upholstery work, where interlining adds padding and body between the cover fabric and the frame.
Why Interlining Matters in Quality
The difference between a garment that holds its shape after a year of wear and one that looks tired after a few months often comes down to how well the interlining was chosen and applied. In shirts, properly fused interlining prevents the collar from curling and developing permanent creases, keeping the garment looking polished wash after wash. In tailored jackets, the interlining through the chest, lapels, and shoulders is what gives the jacket its silhouette. Remove it and the same fabric would drape like a bathrobe.
If you sew your own clothes, testing a small piece of interlining on a fabric scrap before committing to the full garment is worth the extra five minutes. Press it (if fusible) or pin it (if sew-in), then check whether the weight, stiffness, and drape match what you want in the finished piece. That simple test prevents the most common interlining mistakes: too stiff, too floppy, or visible through lightweight fabric.