Spandex (Polyurethane Elastic Fiber / 氨纶 / Elastane / Lycra®)
Spandex (elastane, Lycra®) is a segmented polyurethane elastic fiber — a block copolymer with alternating hard (urethane/urea) and soft (polyether or polyester) segments. The hard segments provide structural integrity through hydrogen bonding; the soft segments provide extraordinary extensibility. The result is a fiber with 400–700% elongation at break and near-100% elastic recovery — properties that make it the essential stretch component in virtually all modern stretch apparel. Spandex is rarely used alone: typically 2–20% is blended with other fibers (cotton, polyester, nylon, wool) to add stretch and recovery to fabrics. Global production is dominated by China, and Lycra® (The LYCRA Company, formerly Invista/DuPont) remains the premium brand.
Quick Facts
| Type | Synthetic segmented polyurethane elastic fiber; block copolymer |
| Chemistry | Hard segment: urethane/urea groups (H-bonded, crystalline); Soft segment: polyether glycol (e.g., PTMEG) or polyester glycol (amorphous, coiled) |
| Commercialized | 1958 (DuPont: Lycra®); originally called "Spandex" (anagram of "expands"); Bayer: Dorlastan® (1964) |
| Spinning method | Dry spinning (DMF or DMAc solvent; ~90% of production) or melt spinning (TPU variant; ~10%); wet spinning rare |
| Global production | ~1.0–1.2 million tons/year; China dominant producer; growing with athleisure and comfort apparel trends |
| Elongation at break | 400–700% (highest of any textile fiber) |
| Elastic recovery | ~95–100% from 50–300% extension; essentially complete recovery |
| Density | 1.0–1.3 g/cm³ (varies with type; polyether ~1.15, polyester ~1.20) |
| Moisture regain | 0.5–1.5% (hydrophobic, but moisture can pass through in blended yarns) |
| Thermal behavior | Softens ~175–200°C; degrades ~230–290°C; heat-sensitive — cannot withstand high-temperature processing |
| Key trade names | Lycra® (The LYCRA Co.), Creora® (Hyosung), Roica® (Asahi Kasei), Dorlastan® (Bayer) |
Properties
| Property | Rating | Engineering implication |
|---|---|---|
| Elongation | ★★★★★ 400–700% | Highest extensibility of any textile fiber; enables stretch garments; the defining spandex property |
| Elastic recovery | ★★★★★ Near-100% | Complete recovery from extension; garments return to original shape; critical for fit and comfort |
| Recovery force / power | ★★★★★ 1.8–2× rubber | Spandex provides stronger recovery force than rubber thread; better garment shaping and support |
| Absolute strength | ★★☆☆☆ Low (0.5–1.0 cN/dtex) | Not a load-bearing fiber; strength comes from the blend partner (cotton, polyester, nylon core) |
| Heat sensitivity | ★☆☆☆☆ Very poor | Degrades above 190°C; cannot survive high-temperature dyeing or finishing; heat-setting at 175–195°C possible with precise control |
| Chemical resistance | ★★★☆☆ Selective | Resistant to dilute acids and alkalis; damaged by chlorine (swimwear limitation); organic solvents can swell or dissolve |
| UV resistance | ★★☆☆☆ Poor | Degrades under sunlight; UV-stabilized grades required for swimwear and outdoor activewear |
| Abrasion resistance | ★★★☆☆ Moderate | Adequate when protected within yarn structure; exposed spandex abrades and breaks down |
Spandex Yarn Types
| Type | Construction | Application |
|---|---|---|
| Bare spandex (裸丝) | Single spandex filament; no covering | Direct knitting (warp knits, circular knits); most common in high-speed production |
| Core-spun yarn (包芯纱) | Spandex core + staple fiber sheath (cotton, wool, polyester) wrapped during ring spinning | Denim (stretch jeans), shirting, chinos; spandex invisible, sheath provides natural look and hand |
| Covered yarn (包覆纱) | Spandex core + filament yarn(s) wound around in opposite directions (single or double covering) | Hosiery, socks, lingerie, swimwear; precise stretch control; durable |
| Air-covered / Intermingled | Spandex + filament yarn combined via air-jet entanglement | Activewear, sportswear; softer than mechanically covered; high productivity |
Advantages vs. Limitations
Advantages
- Unmatched extensibility (400–700%) and recovery (~100%)
- Higher recovery force than rubber (1.8–2×) — better garment shaping
- Lightweight; adds stretch with minimal weight gain (typically 2–10% of fabric)
- Compatible with all major fibers via core-spinning, covering, or co-knitting
- Enables comfort-stretch and power-stretch fabric categories
- Resistant to body oils, perspiration, and detergents
- Long service life when protected within yarn structure
- Fine deniers available (10–20 denier for sheer hosiery; up to 1680 denier for heavy elastic)
Limitations
- Heat-sensitive — degrades above 190°C; limits processing and finishing options
- Chlorine-sensitive — repeated pool/swim exposure degrades spandex (use chlorine-resistant grades)
- Low strength — never used as the primary load-bearing fiber
- UV-degrades — outdoor garments require UV protection
- Cannot be used alone — always blended (2–20%) with other fibers
- Aged spandex loses recovery power (elastane fatigue) — garments eventually "bag out"
- Higher cost than rubber thread (but better performance)
- Dry spinning uses organic solvents (DMF/DMAc) — environmental concern
Yarn Engineering Guide
| Application | Spandex type | Blend partner | Key criteria |
|---|---|---|---|
| Stretch denim (comfort) | Core-spun; 40–70 denier spandex | Cotton (sheath); 2–3% spandex content | Natural look + hidden stretch; ring core-spinning; spandex draft 3–4× |
| Activewear / leggings (power stretch) | Bare or covered; 40–140 denier | Nylon or polyester; 10–20% spandex | High recovery force; opacity; moisture management; UV-resistant if outdoor |
| Swimwear | Covered; chlorine-resistant grade | Nylon (80%) + spandex (20%) typical | Chlorine resistance critical; wet-strength retention; UV-stabilized; firm compression |
| Socks (comfort band) | Covered or core-spun; 20–40 denier | Cotton or nylon body; spandex at cuff | Targeted stretch at welt/cuff; stay-up performance; wash durability |
| Lingerie / intimate apparel | Covered; 10–40 denier | Nylon (body) + spandex for fit | Soft hand; fine denier; uniform stretch; skin-safe dyes and finishes |
| Shirting (stretch) | Core-spun; 20–40 denier | Cotton (sheath); 1–3% spandex | Subtle stretch; natural appearance; spandex must be completely hidden |
Summary
Spandex is the invisible enabler of modern stretch apparel — rarely seen, never used alone, but essential to the comfort and fit of everything from jeans to swimwear. Its engineering is about integration: selecting the right denier, draft ratio, covering method, and blend partner to deliver the target stretch-recovery performance while maintaining the aesthetic and hand feel of the primary fiber. For the yarn engineer, spandex selection is defined by elongation requirement (comfort vs. power stretch), durability environment (chlorine, UV, heat), and integration method (core-spun vs. covered vs. bare). See the Textile Material framework.