Stretch denim is cotton spun with a small percentage of elastane (spandex) — usually 1–3% in B2B specs, up to 4% in fashion fits. The elastane lives in the weft yarn, giving the fabric recovery: it stretches with movement and snaps back instead of bagging.
The Percentage Ladder
| Elastane | Marketed as | Use case |
|---|---|---|
| 0% | Rigid / 100% cotton | Raw denim, heritage, structured fits |
| 1–1.5% | Comfort stretch | Daily wear, kidswear, office fits |
| 2% | Standard stretch | Skinny and slim fits |
| 3–4% | High stretch / super stretch | Jeggings, performance denim |
The Two Failures to Test For
- Growth (bagging): fabric stretches and stays stretched — the sagging knee after one wear. Test: stretch a swatch 20%, release, measure residual growth after 30 and 300 seconds. Acceptable growth is under 3–5%.
- Elastane degradation: chlorine, high heat, and aggressive stone washing break elastane. A stretch jean washed too hard loses recovery permanently — it fits on day one and never again.
Spec Language That Protects You
On your tech pack, write the elastane percentage, the recovery target (<5% growth after 20% extension), and the wash program limits (temperature ceiling, no chlorine bleach). Ask the mill for a 5-cycle wash test report before bulk. A mill that cannot produce this report is guessing.
When 100% Cotton Still Wins
Raw denim lines, selvedge products, and any jean whose story is about aging. Elastane fades differently from cotton and never achieves the same creasing character. Many brands run both: a rigid selvedge flagship plus a comfort-stretch volume line — and clearly label which is which.