Elastic and Elastane Yarn Testing

Elastic yarn testing characterises extension, recovery, power (force at specified extension), and permanent set of bare elastane filaments and covered elastic yarns used in hosiery, swimwear, compression sportswear, and medical compression garments. ISO 20932-1 (determination of elastic properties, CRE tester, gauge length 100 mm, 10 loading-unloading cycles to 80% extension at 100 mm/min): measures force at 80% extension (power, cN/tex — compression garment specifications), permanent set after 10th cycle (elongation remaining at zero load — specification: <5% for garment application, <3% for medical compression), and elastic recovery ER% = (extension − permanent set) / extension × 100. Bare elastane (Lycra, Roica, INVISTA, Bayer) properties: elongation at break 450–650%, tenacity 7–12 cN/tex (lower than polyester but adequate for core function), modulus at 100% elongation 0.5–1.5 cN/tex (determines garment fit tension at 100% body extension). Covered elastic yarn testing (core-spun or covered, 1 or 2 wraps of covering fibre around elastane core): covering tightness (coils per cm of covering yarn measured by optical magnifier — optimum 400–600 coils/m for hosiery, 250–400 for swimwear); core tension during covering (±10% tolerance for uniform fabric tension). Chlorine resistance of elastane in swimwear (ISO 105-E03 adapted, 100 ppm active chlorine solution at 35°C, pH 7.5, 24 hours immersion — polyurethane-based Lycra retains >80% extension after chlorine exposure; polyether Lycra retains >85% — specifying chlorine-resistant grade essential for pool swimwear with 2+ years service life). Heat resistance (bare elastane, dry heat at 160°C 10 min: <5% permanent set indicates adequate thermal stability for heat-setting of elastane-containing fabrics at 180–190°C stenter temperature for 30-second dwell).