Poly-Spandex Blends, Explained

Spandex — also called elastane, and branded Lycra by Invista — is a segmented polyurethane fibre that can be stretched to 5–7× its resting length and snap back. It is expensive, thermally fragile and never used alone in apparel. Blend even 8% of it into polyester and you turn a stable fabric into a stretch fabric.

Two construction routes: (1) bare spandex knitted in as a separate yarn, giving the crispest stretch and best recovery; (2) core-spun spandex, where a spandex filament is wrapped in polyester to hide it — softer hand-feel but slightly less elastic power. Most modern sportswear uses bare spandex on the reverse and polyester on the face.

• Stretch — how far the fabric extends before resisting hard. Set by elastane % and knit tension.
• Recovery — how completely the fabric returns to resting shape after being pulled. A poor recovery fabric bags out at knees, elbows and waistband.
• Modulus — the resistance felt while pulling. High-modulus fabric feels 'firm', low-modulus feels 'soft'. Compression garments need high modulus.
• Set — the permanent deformation left after 100 cycles. Under 3% is athletic grade; over 8% means the garment will bag out within a season.

1. Cut a 100 mm × 50 mm strip parallel to the elastane direction.
2. Clamp both ends in a tensile tester (Instron or equivalent).
3. Extend the strip to 80% of its length at 100 mm/min. Hold for 60 seconds.
4. Release the strip and let it relax for 60 seconds.
5. Measure the new resting length. Recovery = (extended − relaxed) ÷ extended × 100. Athletic grade > 92%.
6. Repeat five times. Recovery must stay above 90% by the fifth cycle.

Elastane does not accept sublimation dye — only polyester does. That means the more elastane in a blend, the paler and less saturated the final print looks, because a smaller fraction of the fibre bed carries colour. In practice:

• 8–12% elastane — sublimates almost like pure polyester, minor colour desaturation, acceptable for kits.
• 15–18% elastane — visible pastel shift; blacks look grey-black, reds look warm-pink. Use higher dye deposit or slightly darker Pantone target.
• 20%+ elastane — sublimation prints look faded. Consider dyeing the polyester first, then knitting, or moving to screen print / DTF for logos.

• Never tumble-dry hot. Heat above 60°C permanently relaxes the elastane.
• Skip fabric softener — it coats the spandex and blocks moisture transport.
• Avoid chlorine unless the fabric is chlorine-resistant grade (special polymer, common in tri-suits).
• Wash inside-out, cool water, mild detergent, hang-dry in shade.
• Store folded flat, not on hangers — hanger stretch = permanent set at the shoulders.