Spandex—also known as elastane (and popularly by the brand name Lycra)—is the stretchy engine inside modern swimwear. Blended with nylon or polyester, it delivers body-hugging fit, freedom of movement, and shape retention.
For most fashion and performance swimwear, a fabric blend of 15%–22% spandex hits the sweet spot; choose nylon/spandex for a soft, premium hand-feel or polyester/spandex for better chlorine/UV resistance and colorfast prints. Avoid heat, hot tubs, and harsh chemicals to keep elasticity alive longer.
What exactly is spandex/elastane?
Spandex (elastane) is a polyurethane-based elastomeric fiber prized for its exceptional stretch and recovery. At the fiber level it can elongate several times its length and snap back—think “micro springs” woven into your fabric.
By itself, spandex isn’t used as a standalone fabric; it’s blended—most often with nylon or polyester—and knitted into 4-way-stretch textiles used in swimwear, activewear, shapewear, and more.
Why it matters in swimwear
Fit & comfort: Molds to the body without restriction.
Recovery: Maintains shape after repeated stretching, swimming, and lounging.
Support: Enables sculpting, compression panels, and secure coverage in water.
How spandex is used in swimwear fabrics
Most swim fabrics are warp-knits (e.g., tricot) or circular knits engineered for 4-way stretch. What you feel on the body is mainly the nylon or polyester face yarn, while the spandex hidden inside provides snap and recovery.
Common compositions (by weight)
- Nylon/Spandex: ~78–85% nylon / ~15–22% spandex
- Polyester/Spandex: ~80–90% polyester / ~10–20% spandex
- Power mesh/powernet liners: may run higher spandex for shaping and support
Typical fabric weights (guidance, not rules)
- 180–200 gsm: lightweight, soft drape, needs careful lining for opacity
- 200–230 gsm: most all-purpose fashion swim
- 230–260 gsm: more coverage, compression, or darker shades that resist show-through
Lining matters: Quality suits often add a tricot or power-mesh lining to improve opacity, comfort, and durability—especially for light colors and white.
Nylon/spandex vs polyester/spandex (and where PBT fits)
| Blend | Feel & Stretch | Chlorine & UV Resistance | Printing | Dry Time | Use Cases |
|---|---|---|---|---|---|
| Nylon/Spandex | Buttery-soft, luxurious hand | Good, but less chlorine-tough than poly | Piece-dye; specialized digital printing | Fast | Fashion swim, premium feel, body-contouring |
| Polyester/Spandex | Slightly firmer hand | Better long-term chlorine/UV than nylon | Sublimation-friendly (vibrant prints) | Fast | Printed collections, team/club swim |
| Polyester (PBT) blends | Firm, stable stretch | Excellent chlorine endurance, often with lower or no spandex | Sublimation-friendly | Very fast | Training/competition suits, long-life pools |
Key takeaways
- Want vivid prints and long pool life? Polyester/spandex (or PBT-rich) is your friend.
- Want a luxury feel and sculpting? Nylon/spandex shines.
- True chlorine warriors often rely on polyester-dominant constructions (sometimes with little or no spandex), trading some softness for longevity.
How much spandex do you really need?
Choosing the right elastane percentage balances stretch, coverage, and lifespan.
Lifestyle/fashion swim: 15–22% spandex for comfort and contour
Performance/compression: 18–25% spandex with engineered patterns and liners
Heavy chlorine exposure (lap pools): consider polyester/PBT-dominant fabrics with lower spandex, or rotate suits to extend life
More elastane ≠ always better. Extremely high spandex + frequent chlorine/hot water can age faster. Fabric construction, face fiber (nylon vs polyester), color, and lining all play a role.
What really degrades spandex ？
Spandex can be sensitive to chlorine, heat, UV, body oils, and some sunscreens. Over time these can break polymer bonds, causing “bagging,” loss of snap, and fabric thinning.
Care tips that extend elasticity
1.Rinse ASAP in cool fresh water after each swim (pool or sea).
2.Hand-wash with mild detergent; avoid bleach and strong stain removers.
3.No wringing, no dryers, no radiators. Heat is the enemy; lay flat or hang to drip-dry in shade.
4.Skip hot tubs or dedicate an older suit for hot tub use.
5.Rotate swimsuits. Alternate wear days to give fibers time to “recover.”
6.Avoid rough surfaces (pool decks, rocks) that can abrade fabric and expose elastic.
Printing & color: what designers should know
- Sublimation printing requires polyester-rich surfaces to bond dyes; it’s the go-to for bright, durable prints with low MOQs and fast lead times.
- Nylon/spandex prints typically use acid/reactive dye routes or transfer/ink systems suited to nylon; they can be gorgeous but often involve different machinery, inks, and lead times.
- Colorfastness in chlorinated water and saltwater is a must-test item; dark or very saturated colors may need extra fixation and thorough post-wash to minimize bleed.
Pro tip: Always approve lab dips and strike-offs on the exact base fabric lot (including elastane percentage and knit structure) you plan to bulk-produce.
Pattern making & construction with elastane
Spandex changes the rules for fit. Good swimwear patterns account for negative ease and fabric modulus—how much force it takes to stretch the textile.
- Negative ease: Garment is smaller than body measurements so it stretches to fit snugly.
- Grading: Size jumps must consider stretch/recovery so larger sizes don’t over-compress and smaller sizes don’t bag out.
- Elastic placement: Quality swimwear use clear elastics or rubber/latex alternatives along leg openings, waist, and necklines for secure seal.
- Stitches: Look for zigzag, coverstitch, or flatlock that can stretch with the fabric; seam threads should be texturized/elastic to avoid popping.
- Reinforcements: Bar-tacks at strap joins; power-mesh for tummy control; foam cups or shelf bras for support as design requires.
Quality & testing checklist for brands
Before you green-light bulk, review samples with a simple test plan:
Stretch & recovery: Check that a 30–50% stretch snaps back without waves or growth.
Opacity when wet: Fit models under bright light and wet-test to avoid show-through.
Pilling & abrasion: Rub tests on seats/underarms where friction is highest.
Seam strength: Gentle tug across seams; no popped stitches or tunneling.
Elastic cycle test: Stretch leg and neckline elastics repeatedly—does the opening grow?
Colorfastness: Quick dips in chlorinated water and saltwater, then dry in shade; check for bleeding or fade.
UPF claim validation: If you advertise UPF 50+, confirm with a reputable lab or supplier documentation.
Care labels: Clear washing/drying icons and fiber content for compliance and returns protection.
Cost & MOQ: how elastane choices affect your budget
Higher spandex content and heavier GSM generally increase fabric cost.
Polyester/spandex can reduce print costs via sublimation, which is fast and scalable.
Color & finish (e.g., rib, crinkle, shimmer) add complexity and may carry higher MOQs or lead times.
Lining, cups, and hardware (boning, underwire, sliders, rings) also move the needle—budget for them early.
For startups, many factories now offer low MOQs (50–100 pieces per style) with tiered pricing; confirm whether MOQs are per color and how size splits are handled.
Quick decision guide
Fashion swim with luxe feel: Nylon/spandex (≈80/20), 200–230 gsm, lined; piece-dye solids or specialty prints.
Printed collections with strong chlorine life: Polyester/spandex (≈85/15), sublimated; 200–230 gsm.
Training/club suits for daily pools: Polyester-dominant (PBT-rich) with low or no spandex; prioritize chlorine endurance and seam strength.
Shaping silhouettes: Heavier gsm + power-mesh panels; spandex ~20–25% total system; robust elastics and bar-tacks.
Light colors/white: Double-line; consider higher gsm and opacity tests when wet.
Frequently asked questions
“Lycra” is a brand name; the generic fiber is elastane (also called spandex). Same family, different naming.“
Most fashion and performance swims target ~15–22% spandex. For heavy chlorine exposure (daily pools), consider polyester-dominant fabrics with lower spandex or rotate suits.
Not always. Beyond a point, more elastane can age faster in heat/chlorine. Balance composition with construction (gsm, lining) and use case.
Sublimation dyes chemically bond to polyester, delivering vivid, durable prints. Nylon printing uses other dye systems and workflows.
Separating elastane from nylon/polyester is technically difficult today. Opt for recycled face fibers, design for long life, and educate customers on care to reduce replacement cycles.
Limit exposure to chlorine/hot water/sun, rinse immediately, air-dry in shade, and avoid dryers.
Conclusion
Spandex is what makes modern swimwear move with you—but the face fiber (nylon vs polyester), fabric weight, lining, and construction determine how that stretch performs in real life.
If your line is print-heavy or destined for chlorinated pools, lean toward polyester/spandex (or PBT-rich) solutions and sublimation. If you want luxury hand-feel and sculpting silhouettes for resort/lifestyle, nylon/spandex blends with thoughtful linings are hard to beat.
Whether you’re building your first capsule or scaling a global line, lock in a test plan, sample on the exact fabric lot, and educate customers on care. Done right, elastane delivers the fit, freedom, and confidence that keep swimmers coming back—season after season.
