Nylon Fiber (Synthetic Polyamide)
Nylon (polyamide, PA) is the world's first fully synthetic fiber, invented by DuPont in 1935 and commercialized in 1938. Its abrasion resistance is the highest of all textile fibers — roughly ten times that of cotton. Combined with high strength, excellent elastic recovery, and the best moisture absorption among major synthetics (2.5–5%), nylon dominates applications where toughness, fatigue resistance, and durability are paramount.
Quick Facts
| Type | Synthetic polyamide (melt-spun from petroleum-based polymer) |
| Chemical structure | Polyamide: repeating amide linkages (–CO–NH–) with methylene chains |
| Invented / commercialized | 1935 (Carothers, DuPont) / 1938 (PA66); 1939 (PA6, IG Farben) |
| Global polyamide production (all uses) | ~8 million tons/year; textile fiber: ~2 million tons |
| PA6 vs. PA66 share | PA6 ~40% of total PA output; PA66 ~30%; together ~70% |
| Key Chinese producer | ~1.3 million tons/year (2014 data); world's second-largest PA producer |
| Density | 1.14 g/cm³ (lighter than polyester at 1.38, cotton at 1.54) |
| Moisture regain | PA6: 3.5–5.0%; PA66: 2.5–4.0% (highest among major synthetics, after vinylon) |
| Melting point | PA6: 215–225°C; PA66: 255–265°C (~40°C higher) |
| Glass transition (Tg) | ~50°C (dry); drops significantly when wet |
| Key trade names | Nylon (DuPont), Perlon (IG Farben, PA6), Cordura, Antron, Tactel (Invista) |
PA6 vs. PA66: The Two Dominant Types
| Property | PA6 (Nylon 6 / 锦纶6) | PA66 (Nylon 66 / 锦纶66) |
|---|
| Monomer(s) | Caprolactam (single, 6 carbons); ring-opening polymerization | Adipic acid + hexamethylene diamine (6+6 carbons); condensation polymerization |
| First commercialized | 1939, Germany (IG Farben: Perlon) | 1938, USA (DuPont: Nylon) |
| Melting point | 215–225°C | 255–265°C (approximately 40°C higher) |
| Strength (cN/dtex) | 3.5–5.5 (standard); high-tenacity: 6.5–8.5 | 4.0–6.0 (standard); high-tenacity: 7.0–9.0 (~20% higher than PA6) |
| Moisture regain | 3.5–5.0% (slightly higher) | 2.5–4.0% |
| Dyeability | Easier; atmospheric pressure possible with acid dyes | More difficult; higher temperature/pressure required |
| Elastic modulus | Lower (softer hand, more flexible) | Higher (stiffer, better dimensional stability) |
| Creep resistance | Moderate | Better (critical for tire cord) |
| Cost (relative) | Slightly lower | Slightly higher |
| Primary textile use | Hosiery, lingerie, swimwear, carpets (dominant in Europe) | High-tenacity industrial yarns, tire cord, parachutes, carpets (dominant in North America) |
Classification
By Chemical Type
| Type | Polymerization route | Key characteristics |
|---|
| PA6 (锦纶6) | Ring-opening of caprolactam (ω-amino acid route) | Most common PA fiber; easier processing; slightly lower melting point; higher moisture absorption |
| PA66 (锦纶66) | Condensation of diamine + diacid (hexamethylene diamine + adipic acid) | Higher melting point, strength, and creep resistance; preferred for industrial and high-temperature applications |
| PA11 / PA12 | From castor oil (PA11, bio-based) or petroleum (PA12) | Lowest moisture absorption among PAs; flexible; expensive; specialty technical uses |
| PA4 / PA46 | Shorter methylene sequences | PA4: high moisture absorption (approaching cotton); experimental; PA46 (Stanyl®): very high melting point (~295°C) |
| PA610 / PA1010 | Longer methylene chains; partly bio-based | Lower moisture absorption than PA6/66; used in monofilaments and specialty textiles |
By Form
| Form | Typical denier / dtex | Primary applications |
|---|
| Fine-denier filament (细旦长丝) | 7–40 denier (0.8–4.4 dtex) per filament | Sheer hosiery, lingerie, lightweight linings |
| Standard filament (普通长丝) | 40–210 denier (4.4–23 dtex) | Sportswear, swimwear, outerwear, linings |
| High-tenacity filament (高强长丝) | 210–1890 denier | Tire cord, ropes, webbing, parachute fabric, conveyor belts |
| Bulked Continuous Filament / BCF | 500–3000 denier | Carpet yarn (largest single nylon textile market by volume) |
| Staple fiber (短纤) | 1.5–6.0 dtex, 38–100 mm | Blends with cotton, wool, or other fibers; carpets; nonwovens |
| Microfiber nylon (超细锦纶) | <1.0 dtex per filament | Luxury lingerie, high-performance sportswear, wiping cloths |
| Textured yarn (弹力丝) | Various; false-twist or air-textured | Stretch apparel, socks, hosiery; adds bulk and elasticity |
By Modification
| Modification | Purpose and mechanism |
|---|
| Antistatic / conductive nylon | Carbon or metal compound incorporation; dissipates static; cleanroom garments, electronics |
| UV-stabilized nylon | UV absorber or stabilizer additives; outdoor textiles, automotive interiors, awnings |
| Flame-retardant nylon | Phosphorus or halogen-based FR additives; LOI 26–30%; protective clothing, upholstery |
| Antimicrobial nylon | Silver-ion or other antimicrobial agents; sportswear, medical textiles, socks |
| Deep-dye / differential-dye nylon | Modified amine-end-group content; produces tone-on-tone effects in carpet and apparel |
| Solution-dyed nylon | Pigment added before spinning; superior colorfastness; carpets, outdoor fabrics |
| Bio-based nylon | PA11 from castor oil (Rilsan®); partially bio-based PA6 and PA66 under development |
Properties
| Property | Rating | Engineering implication |
|---|
| Abrasion resistance | ★★★★★ Best of all fibers | ~10× cotton; ~20× wool; the defining nylon property — ideal for high-wear applications |
| Tensile strength | ★★★★★ Excellent | Standard: 3.5–6.0 cN/dtex; high-tenacity PA66: up to 9.0 cN/dtex; wet strength retained at 85–90% |
| Elastic recovery | ★★★★★ Excellent | ~100% recovery at 3–6% elongation; outstanding fatigue resistance (critical for carpets and dynamic applications) |
| Moisture regain | ★★★☆☆ Moderate (best among major synthetics) | 2.5–5.0%; far better than polyester (0.4%) but below cotton (8%); contributes to comfort vs. polyester |
| Elastic modulus (initial) | ★★☆☆☆ Low | Significantly lower than polyester and cotton; fabric deforms more easily under load — a limitation for apparel requiring shape retention |
| Heat resistance | ★★★☆☆ Moderate (PA6) to Good (PA66) | PA66 tolerates higher temperatures; both types lose strength above 150°C with prolonged exposure |
| UV / light resistance | ★★☆☆☆ Poor (standard) | Degrades under sunlight without stabilization; UV-stabilized grades required for outdoor use |
| Chemical resistance | ★★★★☆ Good | Resistant to alkalis, organic solvents, oils, hydrocarbons; attacked by strong mineral acids and oxidizing agents |
| Dyeability | ★★★★☆ Good | Acid dyes, disperse dyes, reactive dyes possible; PA6 easier than PA66; solution-dyed option for best fastness |
| Thermal behavior | ★★★☆☆ Melts (PA6: ~220°C; PA66: ~260°C) | Melt-drip hazard (like polyester); self-extinguishing tendency better than polyester |
| Static electricity | ★★☆☆☆ Problematic | Lower static than polyester due to higher moisture regain, but still builds up in dry conditions |
Advantages vs. Limitations
Advantages
- Highest abrasion resistance of all textile fibers (~10× cotton)
- Excellent strength; high-tenacity grades reach 9 cN/dtex
- Outstanding elastic recovery and fatigue resistance
- Highest moisture regain among major synthetics (2.5–5%)
- Lightweight (density 1.14 — lighter than PET, cotton, wool)
- Easy to dye with multiple dye classes (acid, disperse, reactive)
- Good chemical resistance (alkalis, solvents, oils)
- Versatile forms: ultra-fine to heavy BCF; staple to high-tenacity filament
- Partially bio-based variants available (PA11 from castor oil)
- Self-extinguishing tendency (better than polyester in flame)
Limitations
- Low initial modulus — deforms easily; poor shape retention in apparel
- Degrades under UV/sunlight without stabilization
- Strength and modulus drop significantly when wet (Tg decreases)
- Melt-drip hazard at relatively low temperatures (PA6: 220°C)
- Higher cost than polyester (approximately 1.5–2×)
- Attacked by strong mineral acids
- Static buildup in dry conditions (though less than polyester)
- Limited heat resistance for prolonged high-temperature exposure
- Fossil-fuel dependent (except PA11 and limited bio-based grades)
- Yellowing tendency with age and light exposure
Yarn Engineering: Selection Guide
| Application | Recommended nylon type | Yarn form | Key criteria |
|---|
| Sheer hosiery / stockings | PA6 fine-denier filament | 7–20 denier monofilament or low-filament-count yarn | Ultra-fine; uniform denier; high luster; good elastic recovery |
| Lingerie & intimate apparel | PA6 or PA66 filament; microfiber | 20–70 denier; 10–68 filaments | Soft hand; drape; good dyeability; often blended with elastane |
| Sportswear / activewear | PA6 or PA66 textured yarn | 40–140 denier DTY; air-textured for cotton-like hand | Abrasion resistance; moisture management; lightweight; UV-stabilized for outdoor |
| Swimwear | PA6 or PA66 + elastane (80/20 typical) | 40–70 denier filament; chlorine-resistant finish | Chlorine resistance; wet-strength retention; quick-drying; UV-stabilized |
| Carpet (residential) | PA6 BCF or staple | 500–1500 denier BCF; solution-dyed | Stain resistance; colorfastness; bulk and cover; cost-competitive |
| Carpet (commercial / high-traffic) | PA66 BCF | 1000–3000 denier BCF; solution-dyed | Higher resilience and crush resistance than PA6; superior appearance retention |
| Tire cord | PA66 high-tenacity filament | 840–1890 denier; 140–280 filaments; dipped | Strength ≥8 cN/dtex; creep resistance; heat resistance; adhesion to rubber (RFL dip) |
| Rope, webbing, slings | PA6 or PA66 high-tenacity filament | 840–6000 denier; twisted or braided | High energy absorption; fatigue life; knot strength retention |
| Parachute / aerospace fabric | PA6 or PA66 ripstop filament | 30–70 denier; high-tenacity; ripstop weave | High strength-to-weight ratio; controlled air permeability; reliability |
| Socks (performance / outdoor) | PA6 or PA66 staple or filament; textured | 1.5–3.0 dtex staple or 70-denier textured filament | Abrasion resistance (heel/toe); moisture management; antimicrobial optional |
| Conveyor belts | PA66 high-tenacity filament | Heavy denier filament; woven fabric | Creep resistance; tensile strength; dimensional stability under load |
Nylon vs. Key Competitors
| Property | Nylon PA6 | Nylon PA66 | PET Polyester | Cotton |
|---|
| Strength (cN/dtex) | 3.5–5.5 | 4.0–6.0 (HT: 9.0) | 3.5–5.5 | 2.5–4.5 |
| Abrasion resistance | ★★★★★ Best | ★★★★★ Best | ★★★★☆ Good | ★★★☆☆ Moderate |
| Moisture regain (%) | 3.5–5.0 | 2.5–4.0 | 0.4 | 7–8.5 |
| Elastic recovery | Excellent | Excellent | Good | Poor |
| Initial modulus | Low | Low–Moderate | High | Moderate |
| Density (g/cm³) | 1.14 | 1.14 | 1.38 | 1.54 |
| Melting point (°C) | 215–225 | 255–265 | 255–265 | Decomposes ~150 |
| UV resistance | ★☆☆☆☆ | ★☆☆☆☆ | ★★★★☆ | ★★★☆☆ |
| Dyeability | ★★★★☆ Easy | ★★★☆☆ Moderate | ★★☆☆☆ Difficult | ★★★★★ Easy |
| Cost (relative) | ★★★☆☆ | ★★★☆☆ | ★☆☆☆☆ (lowest) | ★★★☆☆ |
| Textile fiber output (Mt/yr) | ~2 (total PA textile) | ~78 | ~25 |
Summary
Nylon is the premium synthetic fiber for applications demanding abrasion resistance, elastic recovery, and fatigue life. Its defining quality — unmatched toughness — comes at the cost of low modulus (easy deformation), UV sensitivity, and higher price than polyester. The PA6 vs. PA66 choice is primarily about thermal and mechanical requirements: PA66 for heat, creep, and industrial strength; PA6 for processing ease, dyeability, and hosiery/lingerie. For the yarn engineer, nylon selection centers on the PA type, filament denier, tenacity grade (standard vs. high-tenacity), and modification (UV, FR, antistatic, solution-dyed) that best matches the intended use. See the Textile Material framework for substance–form–performance logic.