Denim, Explained
Denim is a cotton twill with one defining trick: only its lengthwise (warp) yarns are dyed — classically with indigo — while the crosswise weft stays white. That is why jeans are blue on the outside, pale on the inside, and why denim fades so gracefully: indigo clings to the yarn surface and wears away at creases and seats, printing your life onto the cloth.
No other fabric is loved specifically for how it ages.
How denim is made
Warp yarns are rope- or slasher-dyed in repeated quick dips — indigo builds up in layers on the outside of the yarn, leaving the core white (ring dyeing). The yarns are then woven in a sturdy 3x1 twill. Every whisker, honeycomb and worn-in seat on old jeans is that white core surfacing as the indigo layer abrades.
Stretch denim blends a few percent spandex into the weft for fitted cuts. Selvedge denim is woven on narrow shuttle looms whose tidy self-finished edge appears in the outseam cuff — prized in raw-denim culture.
Denim weights
Denim is traditionally measured in ounces per square yard. Roughly: under 9 oz sews shirts and dresses; 10–12 oz is the everyday jeans zone (and the friendliest to home machines); 13 oz up is rigid, warm and slow to break in. Our listings show gsm — multiply ounces by about 34 to convert.
What to sew with denim
- Jeans, obviously — a rite-of-passage sew worth doing once
- Jackets and overshirts
- Skirts, dresses and aprons in lighter weights
- Totes and workwear in heavy weights
Use a jeans needle (90/14–100/16), heavy topstitch thread for the gold stitching, a longer stitch, and flat-felled seams for authentic guts. Hammer or clapper thick seam crossings flat before stitching over them.
Denim vs. chambray
Chambray gets mistaken for lightweight denim constantly, but it is a plainweave — dyed warp, white weft, woven over-under instead of in a twill diagonal. That is why chambray is lighter, smoother and shirt-like. If you can see the diagonal, it is denim.
How to care for denim
Wash cold, inside out, seldom — indigo bleeds by design, especially at first (wash dark alone until the water runs clean). Skip the dryer for fit-critical jeans; heat shrinks and fades. Raw-denim purists wait months before the first wash so the fade sets to the body. That is a culture, not a requirement.
Denim, measured
Fibers in our denim
- Cotton64%
- Polyester63%
- Spandex63%
- Viscose13%
- Nylon5%
- Modal3%
Share of listings containing each fiber — most cloths blend two or more.
Live from 97 measured listings on our shelf. How we measure →
Common questions
Why does denim fade?
Indigo dyes only the surface of the yarn, leaving a white core. Abrasion at knees, thighs and seams wears through the dye layer — the fade map is literally a record of wear.
What weight of denim should I buy for jeans?
10–12 oz (roughly 340–410 gsm) balances durability with sewability at home. Go lighter for summer styles and dresses, heavier for rigid, structured jeans.
Is denim stretchy?
Rigid denim is not. Stretch denim carries 1–3% spandex in the weft for comfort in fitted cuts — check the listing's fiber content and stretch rating.
Does denim shrink?
Untreated cotton denim can shrink 3–5%, mostly in length, on a hot wash. Pre-wash yardage twice for jeans, and keep finished garments out of hot dryers.
