Everything you sew, dye, or print starts as fabric — and fabric behaves the way it does because of how it was built. A T-shirt curls at the hem, a polo collar holds its shape, and a pair of leggings springs back, all for structural reasons that have nothing to do with fibre content.
Understanding that structure is what lets you predict how a fabric will behave before you cut into it. This guide covers how knits and wovens differ, what GSM actually tells you, the main knit and weave structures, and how yarn and thread choices feed into all of it.
It’s the starting point for everything in our knitting and fabric section.
Knit vs Woven: The Fundamental Split
Nearly all fabric falls into one of two families, and the difference determines almost everything about how it behaves.
Woven fabric is made from two sets of yarn crossing at right angles — warp running lengthwise, weft running across. The yarns are essentially straight, interlacing over and under each other. Because the yarns don’t move much, woven fabric has little inherent stretch. It’s stable, holds a crisp edge, and frays when cut.
Knitted fabric is made from a single yarn formed into interlocking loops. Loops can deform and recover, which is where knit stretch comes from — not from the fibre, but from the geometry. This is why 100% cotton jersey stretches while 100% cotton poplin doesn’t. Same fibre, different structure.
The practical consequences run right through everything:
| Woven | Knit | |
|---|---|---|
| Stretch | Minimal (unless elastane added) | Substantial, inherent |
| Cut edges | Fray | Curl or run, don’t fray |
| Seam needs | Standard straight stitch | Stretch stitch or overlock |
| Needle type | Sharp | Ballpoint |
| Drape | Structured | Fluid, body-conforming |
| Typical use | Shirts, trousers, jackets, denim | T-shirts, underwear, activewear |
Sewing a knit with a straight stitch and a sharp needle is one of the most common beginner mistakes — the seam pops when the fabric stretches, and the sharp needle cuts the knit loops, causing ladders.
Understanding GSM
GSM means grams per square metre — the weight of the fabric, not its thickness or quality.
It’s the single most useful specification because it predicts a great deal: drape, opacity, warmth, durability, and how the finished garment will hang.
Rough guidance for cotton jersey:
| GSM | Character | Typical use |
|---|---|---|
| 120–150 | Very light, often semi-sheer | Summer tops, linings |
| 150–180 | Light | Standard fashion tees |
| 180–220 | Medium | Everyday T-shirts, the most common range |
| 220–260 | Heavy | Premium tees, long sleeves |
| 260–320 | Very heavy | Sweatshirts, structured garments |
What GSM doesn’t tell you is quality. A 200 GSM fabric made from coarse open-end yarn is a different product from a 200 GSM fabric made from combed ring-spun yarn, despite weighing identically. Weight tells you about substance; yarn and construction tell you about feel and longevity.
The same GSM in a different structure also behaves differently — 150 GSM in plain weave is crisp and wrinkles readily, while 150 GSM in twill is softer and more durable.
Knit Structures
Single Jersey
Single jersey is knitted on one needle bed, producing a fabric with a smooth face and a looped back — the two sides look clearly different. It’s the most common knit in the world and the default T-shirt fabric.
It’s light, drapes well, and stretches mainly across the width. Its defining quirk is that cut edges curl toward the face, which is why jersey hems need proper finishing and why cutting jersey accurately takes more care than cutting woven fabric.
Typical weight sits around 130–220 GSM.
Interlock (Double Jersey)
Interlock uses two needle beds with loops interlocking between them, effectively producing two jersey layers joined together. The result looks identical on both sides and doesn’t curl at the edges.
It’s denser, more stable, and holds its shape better than single jersey, at the cost of being heavier and warmer. That stability is why it’s favoured for polo shirts, school uniforms, children’s clothing, and anywhere dimensional consistency matters.
Typical weight runs 180–320 GSM.
Rib
Rib knits alternate knit and purl columns, producing visible vertical ribs on both faces. The structure gives dramatic crosswise stretch and strong recovery — it pulls back into shape rather than staying stretched.
That recovery is exactly why rib is used for cuffs, collars, and waistbands. Common variants are 1×1 and 2×2, referring to the alternation pattern.
Pique
Pique has a textured, slightly raised surface with a fine geometric pattern. It’s the classic polo shirt fabric — more breathable than flat jersey because of its surface texture, and more resistant to showing creases.
French Terry and Fleece
Both have loops on the back. French terry leaves the loops intact, giving a soft, absorbent back that’s still relatively light. Fleece brushes those loops into a soft nap, trapping air and adding considerable warmth.
French terry works year-round; fleece is squarely a cold-weather fabric.
Adding Elastane
Adding a small percentage of elastane — typically 5% — transforms recovery. Cotton jersey stretches but gradually bags out; cotton-elastane jersey springs back. This is why fitted garments, leggings, and activewear almost always include elastane, and why they’re more heat-sensitive during pressing and dyeing.
Our fabric types and specs section covers these structures and their specifications in more depth.
Weave Structures
Plain Weave
The simplest possible interlacing — each weft yarn passes over one warp, under the next. Maximum interlacing points make it strong and stable, but it creases readily and has no inherent stretch. Poplin, muslin, chambray, and canvas are all plain weaves at different weights.
Twill
Twill offsets the interlacing points, producing a visible diagonal line across the fabric. Fewer interlacings mean the yarns can pack more densely, which makes twill stronger and more drapey than plain weave at the same weight, and better at hiding soil and wrinkles.
Denim is the best-known twill. Gabardine, chino, and herringbone are others.
Satin and Sateen
These minimise interlacing further, letting long yarn floats sit on the surface. The result is smooth, lustrous, and fluid. The tradeoff is fragility — those long floats snag easily and abrade faster.
Technically, satin uses filament yarn (silk, polyester) and sateen uses spun yarn (usually cotton), but the structural principle is the same.
Hand Knitting and Crochet
Hand knitting and crochet produce fabric the same way industrial knitting does — through interlocking loops — just one stitch at a time.
Knitting uses two needles and holds live stitches on the needle throughout. Crochet uses a single hook with one live loop, making it easier to work in three dimensions and easier to undo, but generally slower and more yarn-hungry.
Core knitting skills are few: casting on, the knit stitch, the purl stitch, increasing, decreasing, and casting off. Almost every pattern is a combination of these. Knit and purl together produce the basic structures — all knit gives stockinette (which curls, exactly like machine jersey), alternating gives garter or rib depending on the arrangement.
Gauge — stitches and rows per 10cm — is the detail beginners skip and later regret. Patterns are written to a specific gauge, and knitting at a different tension produces a garment in a completely different size. Knitting a gauge swatch before starting is genuinely worth the twenty minutes.
Our knitting basics and techniques section covers stitches, patterns, and technique in detail.
Yarn and Thread
Yarn characteristics carry through into whatever’s made from them.
Fibre sets the fundamental properties — cotton is breathable and absorbent but slow to dry; wool insulates even when damp and resists odour; linen is strong and cool but creases; polyester is durable and quick-drying but less breathable; acrylic mimics wool cheaply with less warmth.
Yarn count describes thickness. In the Ne (English cotton) system used for most cotton yarn, higher numbers mean finer yarn — 30/1 is finer than 20/1. Finer yarn generally produces softer, smoother fabric.
Spinning method matters more than most people expect. Open-end (rotor) spinning is fast and cheap but produces a coarser, weaker yarn. Ring spinning produces smoother, stronger yarn. Combed ring-spun removes short fibres first, giving the smoothest, most durable result. Two fabrics at identical GSM can feel entirely different because of this.
Ply is how many strands are twisted together — single-ply is softer but pills more readily; multi-ply is stronger and more durable.
For sewing thread specifically, weight runs inversely as well: 50wt is standard general-purpose, 40wt is heavier for topstitching, 30wt heavier still for visible decorative work.
More on this in our yarn and thread section.
Quilting
Quilting joins three layers — top, batting, backing — with stitching that holds them together. The top is usually pieced from many fabric sections; the batting provides loft and warmth; the stitching is both structural and decorative.
Quilting cotton is a specific product: plain weave, typically 110–150 GSM, tightly woven, stable, and pre-shrunk. Its stability is exactly why it’s used — pieces need to hold their exact dimensions through repeated handling.
Batting choice drives the finished character: cotton batting is flat and drapes densely, polyester is lofty and light, wool is warm and springy, bamboo blends fall in between.
The two persistent technical challenges are accurate seam allowance (the standard quarter-inch, where small errors compound dramatically across a pieced block) and managing bulk through the machine, which is where throat space and a walking foot earn their keep.
Our quilting section goes into patterns, techniques, and tools.
Choosing Fabric for a Project
Work through these in order:
- Knit or woven? This is set by the garment. A fitted T-shirt needs knit; a tailored shirt needs woven. Substituting one for the other rarely works, because patterns are drafted assuming a specific amount of stretch.
- Weight (GSM)? Match to season, drape, and opacity. Hold fabric up to light if you’re unsure about sheerness.
- Fibre? Comfort, care, and cost. Natural fibres breathe better; synthetics are more durable and easier to care for; blends compromise deliberately.
- Stretch and recovery? Check both. Fabric that stretches but doesn’t recover will bag at knees and elbows.
- Shrinkage? Pre-wash natural fibres before cutting. Cotton knit can shrink 5–10% on first wash, which is the difference between a garment that fits and one that doesn’t.
Common Problems
Cut jersey edges curl so badly I can’t sew straight. Inherent to single jersey. Use plenty of pins or clips, a walking foot, and consider stabilising the hem with fusible tape.
My knit seams pop when stretched. Straight stitch has no give. Use a stretch stitch, narrow zigzag, or an overlocker.
Ladders running up my knit fabric. A sharp needle cut the loops. Ballpoint needles push between loops instead.
The garment fitted before washing and now doesn’t. Unwashed fabric shrank after construction. Always pre-wash.
My knitted piece is the wrong size despite following the pattern. Gauge mismatch. Your tension differs from the pattern’s, so every stitch is slightly wider or narrower and the error compounds.
Fabric looked right online but feels wrong. GSM and fibre content don’t capture hand-feel. Order swatches for anything significant.
Where to Go From Here
- Fabric Types & Specs — GSM, weaves, knit structures and how to read a fabric specification
- Knitting Basics & Techniques — stitches, patterns and technique from beginner onward
- Quilting — patterns, batting, piecing and finishing
- Yarn & Thread — fibre types, counts, plies and choosing thread
Related areas:
- Fabric Dyeing — fibre content determines which dyes will work
- Fabric Printing — fabric structure affects which printing methods are viable
- Apparel & Clothing — how fabric choices show up in finished garments
Frequently Asked Questions
What does GSM actually mean, and what’s a good number? Grams per square metre — fabric weight. There’s no universally “good” number; it depends on use. Around 180–220 GSM is standard for everyday T-shirts, 260+ for sweatshirts, 120–150 for lightweight summer fabrics. Higher GSM means more substantial, not necessarily better quality.
Why does my T-shirt fabric curl at the edges? Because it’s single jersey. The structure is unbalanced — the face and back are built differently, so cut edges roll toward the face. It’s normal and unavoidable in single jersey. Interlock and rib don’t curl, which is one reason they’re used for collars and cuffs.
What’s the difference between single jersey and interlock? Single jersey is knitted on one needle bed — smooth face, looped back, lighter, stretchier, curls at the edges. Interlock uses two needle beds — identical on both sides, heavier, more stable, doesn’t curl. Interlock costs more and is chosen where shape retention matters.
Do I need to pre-wash fabric before sewing? For natural fibres, yes. Cotton and linen shrink significantly on first wash, and a garment constructed from unwashed fabric will shrink out of fit. Wash and dry exactly as you’ll treat the finished garment. Polyester shrinks minimally, so pre-washing matters less.
Why is my knitting the wrong size even though I followed the pattern? Gauge. Patterns assume a specific number of stitches and rows per 10cm, and everyone knits at a slightly different tension. If your gauge is looser, every stitch is wider and the piece comes out larger. Knit a swatch first and change needle size until your gauge matches the pattern’s.
Is higher thread count better? Up to a point, then it becomes marketing. Above roughly 400, manufacturers often reach high numbers by counting plies within yarns rather than using genuinely finer yarn. Fibre quality and weave matter more than the number on the package.
What’s the difference between combed and carded cotton? Carding cleans and aligns fibres. Combing adds a further step that removes the shorter fibres, leaving only longer ones. Combed cotton is smoother, stronger, and pills less — and costs more. On a T-shirt label, “combed ring-spun” indicates a noticeably better fabric than plain “cotton” at the same GSM.
