Fusible interfacing has a heat-activated adhesive on one side and is pressed onto the wrong side of the fabric, which is quick and gives a crisp, stable result on cottons, linens, poplin, denim and bag fabrics. Sew-in interfacing has no adhesive and is basted into the seam allowances, so it keeps the natural hand of the fabric and is the right choice for sheers, textured and napped fabrics, anything that cannot take a hot iron, and traditional tailoring. For most garments and all bags, fusible is the practical default; switch to sew-in when the fabric says so.
| Feature | Fusible interfacing | Sew-in interfacing |
|---|---|---|
| How it attaches | Heat-activated adhesive, pressed on | Basted or stitched inside the seam allowance |
| Time | Minutes per piece | Longer; each piece is pinned and basted |
| Effect on the fabric | Stiffer, crisper; can change the hand | Keeps the fabric's drape and hand |
| Fabrics it suits | Cotton, linen, poplin, denim, canvas, stable knits | Sheer, lace, velvet, sequins, vinyl, some synthetics, loose weaves |
| Risk | Bubbles, shrinkage, adhesive showing through | Shifting between layers if not basted well |
| Removable | No | Yes, until the seams are sewn |
| Available as | Woven, non-woven, knit (tricot) | Woven, non-woven, hair canvas, silk organza |
| Cost tier | Entry-level | Entry-level to mid; hair canvas costs more |
What does interfacing do?
Interfacing is a layer of fabric added to the wrong side of a garment piece to give it body, stability or shape: it stops a buttonhole from stretching, keeps a collar crisp, holds a waistband straight and stops a neckline facing from rolling to the outside. It is used in collars, cuffs, plackets, facings, waistbands, pocket openings, and across the whole body of bags and hats. It comes in weights from sheer to stiff, and in woven, non-woven and knit constructions, each of which is sold both as fusible and as sew-in.
What is the difference between fusible and sew-in interfacing?
A fusible interfacing has dots or a web of adhesive on one side. You lay it adhesive side down on the wrong side of the fabric and press with a hot iron and steam for 10 to 15 seconds in each spot; the adhesive melts into the fabric and the two become one layer. The piece is then cut and sewn as a single layer, which is why it is faster and why the result is so stable.
A sew-in interfacing is cut the same shape, laid on the wrong side of the piece, pinned and basted inside the seam allowance, and then caught in the seams as the garment is sewn. The two layers stay separate between the seams, so the fabric drapes as it did before, and the interfacing can be trimmed out of the allowances after the seam is sewn to reduce bulk.
Which fabrics need sew-in interfacing?
Use sew-in when fusing would damage the fabric, show through it, or fail to stick:
- Sheer and lightweight fabrics such as chiffon, organza, voile and lace, where the adhesive dots show as a shadow and fusible stiffens the fabric out of character. Silk organza as a sew-in is the classic choice.
- Napped and textured fabrics such as velvet, corduroy, bouclé, terry and seersucker, where the pressing needed to fuse crushes the surface, and the adhesive only touches the high points.
- Heat-sensitive fabrics: vinyl, faux leather, sequins, some acetates and nylons, and anything that melts or shines under an iron at the cotton setting.
- Loosely woven fabrics such as open-weave linen and tweed, where the adhesive bleeds through to the right side.
- Water-repellent or coated fabrics, which the adhesive does not bond to.
- Tailored jackets and coats in the traditional method, where hair canvas is pad-stitched by hand to shape the chest and lapel. Sewly does not draft tailored jackets with lapels yet, but the same sew-in approach applies to the shaped front of a structured kimono jacket in a heavy fabric.
Everything else, which covers most dressmaking, takes fusible well.
How do you fuse interfacing properly?
Most problems with fusible interfacing come from the pressing, not the product.
- Pre-shrink both the fabric and the interfacing. Fusible interfacing shrinks under the iron's steam; soak it in warm water for ten minutes, roll in a towel and let it dry flat, or press it with steam, hovering, before cutting.
- Cut the interfacing the same shape as the piece, or 3 mm (1/8 in) smaller on each side so no adhesive reaches the ironing board.
- Place it adhesive side down (the side that feels rough or shows dots) on the wrong side of the fabric. Cover with a damp pressing cloth.
- Press, do not iron. Lower the iron, hold for 10 to 15 seconds with steam, lift, move to the next overlapping spot. Sliding the iron shifts the layers and causes bubbles.
- Turn the piece over and press again from the fabric side.
- Let it cool flat before moving it. The bond sets as it cools.
Test on a scrap first, every time: the right heat setting, the right time and whether the adhesive shows through are all specific to the fabric and the interfacing you have. The scrap also tells you whether the fused piece has the body you want or has gone board-like.
Which weight and type of interfacing should you use?
The interfacing should be the same weight as the fabric or lighter, never heavier. A rule that works: hold the fabric and the interfacing together and let them drape over your hand; the pair should still move like the fabric, only crisper.
- Woven interfacing has a grain and behaves like a fabric. Cut it on the same grain as the piece. Best for shirt collars, cuffs and anything where a crisp but fabric-like result matters.
- Non-woven interfacing is pressed fibers with no grain, cut in any direction, cheap and stable. Best for facings, waistbands, bags and crafts. It can look papery on fine fabric.
- Knit (tricot) interfacing stretches one way and is soft. Best for knits, for lightweight wovens where you want gentle support, and under buttonholes on jersey.
- Weft-insertion interfacing is a knit with woven threads added, soft and drapey with good stability: the all-rounder for dresses and jackets in medium fabric.
For buttonholes on a shirt front, a light woven fusible on the placket is enough. For a tote bag that stands up on its own, a heavy non-woven fusible on the outer pieces or a fusible fleece gives the structure, and sew-in foam stabilizer gives even more.
Can you combine fusible and sew-in interfacing?
Yes. A common combination is a light fusible across a whole bag or collar piece for stability, with a sew-in stiffener or canvas in the parts that need shape, such as a bag base or a stand collar. Another is a sew-in interfacing in a sheer collar with a light fusible in the enclosed facing, where it never shows. Avoid fusing over a sew-in layer; fuse first, then add the sew-in on top.
Which should you choose?
- Cotton, linen, poplin, chambray, denim, canvas: fusible, woven for collars and cuffs, non-woven for facings and waistbands.
- Knits (T-shirts, sweatshirts, ponte dresses): knit or tricot fusible, on necklines, plackets and under buttonholes only.
- Sheer and lightweight fabrics: sew-in silk organza or a sheer sew-in nylon.
- Velvet, corduroy, bouclé, terry: sew-in, basted in with the layers kept flat.
- Vinyl, faux leather, sequins, coated fabric: sew-in, or no interfacing at all if the fabric already has body.
- Bags, hats, pouches: fusible non-woven, fusible fleece or foam stabilizer; the stiffer, the more it stands up.
- Tailored jacket or coat: sew-in hair canvas in the front, fusible weft-insertion elsewhere.
The notions list on each Sewly pattern says how much interfacing a garment needs for its facings, waistband or collar, so you can buy the right quantity in the type that suits your fabric. When you are unsure, make the sample: a 15 cm (6 in) square of fabric fused with your candidate, washed once and dried, tells you more than any chart.