What Is Denim? Twill Weave, Weights and Raw vs Selvedge Explained

What is denim fabric?

Denim is a durable cotton fabric woven in a twill structure, with the lengthwise warp yarns dyed blue with indigo and the crosswise weft yarns left white or ecru. Because a twill floats each warp yarn over several weft yarns, the face of the cloth is mostly blue and shows diagonal lines, while the reverse is mostly white. That two-tone build is what makes denim fade into the patterns people love.

Jeans are only one product. Denim is also used for jackets, shirts, skirts, workwear, bags and even sofa covers, and you will find decorative ideas such as back-pocket embroidery on many styles.

Where does the name come from?

The word denim is usually traced to serge de Nimes, a sturdy twill from the French city of Nimes, while the word jeans links to Genoa, whose sailors wore a heavy cotton cloth. In 1873 Levi Strauss and tailor Jacob Davis patented copper rivets for work trousers, and blue denim workwear grew into the most worn garment in the world.

How denim is made

Good denim depends on two things: how the indigo is applied and how the cloth is finished. In rope or slasher dyeing, warp yarns pass through indigo baths many times and oxidise in the air between dips. Indigo does not penetrate deep into cotton, so the yarn stays white at its core. When the surface rubs away through wear, that white core shows through as fades and whiskers.

Sanforizing is a compressive shrinkage process that pre-shrinks the fabric so finished jeans stay close to their size after washing. Skewing twists the cloth slightly so the legs do not spiral around your shins after a few washes.

Types of denim you will see on labels

Raw (dry) denim

Raw denim has not been washed after weaving. It is stiff, dark and starchy at first, then softens and fades according to how you move. If it is also unsanforized, expect noticeable shrinkage on the first soak.

Selvedge denim

Selvedge (self-edge) denim is woven on older shuttle looms that make narrow cloth with clean, finished edges. On jeans you see that edge on the outseam when you turn up the cuff, often with a coloured line. Selvedge is a weaving method, not a sign that the fabric is raw.

Stretch denim

Adding 1 to 3 percent elastane to the weft makes skinny and slim jeans comfortable. It also makes them more prone to bagging at the knee and less durable over time, especially when dried hot.

Right-hand, left-hand and broken twill

Most denim is right-hand twill, with diagonal lines running up to the right. Left-hand twill feels softer, and broken twill alternates direction to reduce leg twist.

Coloured and black denim

Black and grey denim usually uses sulphur dyes, which fade to a greyish tone. Coloured denim uses other dye classes and fades differently from indigo.

Denim weights explained

Weight is quoted in ounces per square yard of unwashed fabric. It affects how a garment drapes, breathes and wears.

Denim vs other cotton fabrics

• Chambray also uses a coloured warp and white weft, but it is a lighter plain weave without diagonal lines.
• Drill and chino twill are twills dyed in the piece, so both sides are the same colour.
• Canvas is a heavy plain weave, stiffer and flatter than denim.

For a broader comparison of fibres and constructions, see our fabric types and specifications guide.

How to read a denim label

• Weight (oz): heavier denim lasts longer but takes longer to soften.
• Sanforized or unsanforized: unsanforized raw denim needs sizing up or a pre-soak.
• Composition: 100% cotton for rigid jeans; 98% cotton, 2% elastane for comfort stretch; higher elastane or polyester for super-stretch styles.
• Selvedge: look for the clean edge with a coloured line on the outseam when you turn up the cuff.
• Wash: rinse, stone, enzyme or bleach washes change colour and softness, not the base fabric.

Can you dye faded denim?

Yes. Cotton denim can be re-dyed at home with cotton dyes (fibre-reactive or all-purpose dyes) or with a home indigo kit for a true blue. Two things surprise people. First, most jeans are sewn with polyester or poly-core thread, so the topstitching stays its original colour. Second, stretch denim often contains polyester or elastane that takes cotton dyes poorly, so the result can look heathered. Wash the jeans first to remove finishes, dye them wet, and rinse until the water runs clear.

Why jeans twist and fade the way they do

Twill weave and the yarn’s twist pull the fabric slightly off-grain, which can make side seams rotate toward the front of the leg. Good mills counter this by skewing the fabric before cutting. Fading follows your body: whiskers at the hips, honeycombs behind the knees, and lighter areas on the thighs, because indigo sits on the yarn surface and wears away where you move and rub most.

How to wash and care for denim

• Wash less often; air jeans between wears and spot clean marks.
• Turn jeans inside out, wash cold with dark-colour detergent, and wash new dark denim alone for the first few cycles.
• Line dry where possible. Hot tumble drying adds shrinkage and weakens elastane.
• For softer jeans without harming fades, see our picks of fabric softener for jeans, and use it sparingly on stretch denim.
• Soak unsanforized raw denim in lukewarm water before hemming so the length settles first.

Is denim sustainable?

Conventional cotton farming, indigo dyeing and garment washing use large amounts of water, energy and chemicals. Better options include organic or recycled cotton, foam or nitrogen indigo dyeing, laser and ozone finishing instead of stone washing, and simply wearing jeans longer and washing them less. Denim is also one of the easiest fabrics to repair, so patching and darning extend its life considerably.

Frequently asked questions