Introduction
Nylon 6 (PA6) and Nylon 66 (PA66) are the two most widely used polyamides. They look similar on a datasheet, yet their molecular structures create real differences in strength, heat resistance, moisture response, processing and cost.
Engineers, product designers, manufacturers and procurement teams often struggle to decide which one is "better" for a given part. There is no single answer. A glass-filled PA66 grade can win on heat deflection while a PA6 grade wins on notched impact, as the matched BASF datasheets below show.
This article compares properties, applications and selection criteria so you can match the polymer to the job, not to a rumour.
Key Takeaways
- Both polyamides offer strength, toughness, wear resistance and electrical insulation.
- PA66 usually leads on stiffness, heat resistance and creep, depending on grade.
- PA6 often suits impact, flexibility, appearance and processing.
- Choose based on temperature, humidity, chemicals, load, tolerances and compliance.
Nylon 6 and Nylon 66: Structure and Core Characteristics
What the names mean
Both are semi-crystalline polyamides. The numbers refer to carbon counts in the monomers.
- Nylon 6 is made by ring-opening polymerisation of caprolactam, a single monomer with six carbons.
- Nylon 66 is made by condensation of adipic acid and hexamethylenediamine, each with six carbons. Water is released as the amide bond forms.
Structure and behaviour
BASF describes partially crystalline polyamides where hydrogen bonding between chains adds strength and heat resistance, while flexible amorphous regions add toughness. Hydrogen on the amide nitrogen interacts with oxygen on neighbouring chains, restricting chain movement.
These are tendencies, not guarantees. Molecular weight, polymerisation conditions, moisture state, additives and reinforcement all shift the real numbers.
Commercial forms
The same polymer family serves very different markets:
- Textile and carpet yarn, industrial yarn and tyre cord
- Packaging film
- Injection-moulding pellets, unfilled and glass-reinforced
- Machined rods, tubes and plates
Fibre denier, orientation and processing change performance, so resin data cannot be read straight across to yarn.
Nylon 6 and Nylon 66 Properties Compared
Shared properties
Both materials provide:
- Tensile strength and toughness
- Abrasion resistance and fatigue performance
- Low friction
- Resistance to oils and many fuels
- Electrical insulation
- Light weight (density about 1130 kg/m³ unfilled)
Mechanical performance
The table uses BASF Ultramid datasheet values (D/C = dry/conditioned). These are grade values, not polymer-wide guarantees.
| Property | PA6 B3S | PA66 A3K | PA6-GF30 B3EG6 | PA66-GF30 A3EG6 |
|---|---|---|---|---|
| Tensile modulus, MPa, D/C | 3500/1200 | 3000/1100 | 9500/6200 | 10000/7200 |
| Tensile stress, MPa, D/C | Yield 90/45 | Yield 85/50 | Break 185/115 | Break 190/130 |
| Notched Charpy 23 °C, kJ/m², D/C | 4/50 | 5/20 | 15/30 | 11/20 |
Yield stress and stress at break are different endpoints, so compare only within the unfilled pair or the GF30 pair. Dry unfilled PA6 actually shows higher yield stress than PA66 here. Conditioned PA66 holds up better, and glass-filled PA66 keeps more modulus after conditioning (7200 vs 6200 MPa).
Thermal performance
| Property | PA6 B3S | PA66 A3K | PA6-GF30 | PA66-GF30 |
|---|---|---|---|---|
| Melting point, °C | 220 | 260 | 220 | 260 |
| HDT 1.8 MPa, °C | 65 | 75 | 210 | 250 |
| HDT 0.45 MPa, °C | 180 | 220 | 220 | 260 |
| IEC 60216 index, °C (20,000 h) | 87 | 101 | 135 | 135 |
This is why PA66 is the usual choice for hotter service. Keep three things apart: melting point, short-term heat deflection and long-term ageing. Continuous-use temperature and UL 746B RTI are not listed with the melting-point and HDT figures above, so confirm those values with the supplier for your grade.
Moisture, dimensions and electrical behaviour
Both absorb water, and it changes dimensions, stiffness, impact, creep and electrical performance. The B3S modulus drops from 3500 to 1200 MPa when conditioned, while its notched Charpy rises from 4 to 50 kJ/m².
- Equilibrium moisture at 23 °C/50% RH: PA6 2.6-3.4%, PA66 2.5-3.1%
- GF30 grades: PA6 1.9-2.3%, PA66 1.5-1.9%
- Dissipation factor at 1 MHz (conditioned): PA6 3000 vs PA66 2000 (×10⁻⁴)
Geometry, humidity and conditioning time all change the outcome.
Chemical and environmental resistance
BASF reports resistance to lubricants, fuels, hydraulic fluids, coolants and aqueous alkalis and salts. Limits include zinc chloride, concentrated mineral acids and some oxidants or chlorinated hydrocarbons, especially when hot.
UV and heat-ageing performance come from stabilised grades, not the base polymer. Always test against the exact chemical, concentration, temperature, duration and grade.
Processing and cost
| Grade | Melt, °C | Mould, °C | Shrinkage (parallel/normal), % |
|---|---|---|---|
| PA6 B3S | 250-270 | 40-60 | 0.90/0.90 |
| PA66 A3K | 280-300 | 60-80 | 1.50/1.80 |
| PA6-GF30 | 270-290 | 80-90 | 0.25/0.70 |
| PA66-GF30 | 280-300 | 80-90 | 0.53/1.02 |
Higher shrinkage and processing temperatures in PA66 affect tooling, warpage and energy use. ICIS identifies feedstock and energy volatility as the main nylon cost drivers, so request current quotes rather than assuming a fixed PA66 premium.
Nylon 6 and Nylon 66 Uses and Applications
Nylon 6 applications
- Clothing yarn and carpets: appearance, dyeability and toughness
- Packaging film: flat and tubular food-packaging films
- Industrial yarn and bias tyre cord: SRF supplies PA6 cord for bias truck, bus and off-the-road tyres
- Cable jacketing: UV-stabilised grades
- Engine components, radiator tanks, circuit breakers, machinery parts: LG Chem lists these uses for its LUMID PA6
Nylon 66 applications
- Airbags: high-tenacity PA66 yarn for side and curtain airbags
- Under-bonnet parts: charge-air coolers, cylinder-head covers and intake manifolds
- Connectors, gears, bearings, bushings: stiffness, wear and heat retention
- Heavy-duty tyre cord and machined stock
PA66 is not automatically right for every demanding job. Moisture, impact, chemical exposure, cost and processing still need checking. In notched Charpy impact, a typical PA6-GF30 grade can outperform its PA66 counterpart.
Reinforced and modified grades
- Glass fibre: PA6 modulus rises from 3500 to 9500 MPa, PA66 from 3000 to 10000 MPa
- Mineral filler: medium rigidity and low warpage (BASF B3M6)
- Impact modifier: high dry and low-temperature impact (A3Z)
- Heat stabiliser: better heat-ageing resistance
- Flame retardant: UL 94 results change with thickness; one PA66-GF25 grade is HB at 0.60 mm and V-0 at 0.81 mm
Compare a filled grade with a similarly filled grade of the other polymer, never with an unfilled one. LG Chem's LUMID range, for example, spans standard, reinforced and flame-retardant PA6 and PA66 grades.
Industry selection notes
- Automotive: under-bonnet heat and load favour glass-filled PA66, though PA6 is used in radiator tanks and structural parts
- Electrical and electronics: check flame rating and tracking, not just polymer type
- Wire and cable: PA6 jacketing, PA66 harness parts
- Packaging, textiles, agriculture: PA6 films and yarns dominate
- Healthcare and food contact: certification is grade-specific; the FDA evaluates the final device, not base resin, and USP Class VI status is not automatic
How to Choose Between Nylon 6 and Nylon 66
Match the polymer to the dominant requirement
Consider PA66 when heat resistance, stiffness, creep resistance and sustained wear dominate. Consider PA6 when impact, flexibility, appearance, processability or cost balance matter more.
"Which is stronger?" PA66 often has higher stiffness and heat performance, but grade, reinforcement, moisture state, test method and design decide it.
Evaluate the service environment
Before choosing, list:
- Operating temperature and humidity
- Water and chemical contact
- UV exposure
- Cyclic loading, impact and friction
- Dimensional tolerances
- Electrical requirements
Validate before production
- Compare supplier datasheets at the same test state
- Run application-specific tests
- Review mould-flow and shrinkage behaviour
- Check compliance, recycled-content and traceability needs
Processing, Sustainability and Sourcing Considerations
Processing and moisture control
Dry resin matters. BASF specifies 80 °C for 4 hours and 0.03-0.06% residual moisture for A3EG6. Toray links wet pellets to silver streaks, voids and reduced molecular weight.
Watch for:
- Splay and internal voids from wet resin
- Warpage from fibre orientation, wall thickness and gating
- Dimensional drift as parts absorb moisture
- Inconsistent properties between batches
Supplier processing windows are guidance. Confirm them with trials.
Formulation, scale-up and sustainability
Fillers, stabilisers, colourants and recycled content all affect performance and recyclability. Recycling routes exist, including Aquafil's ECONYL PA6 from fishing nets and carpets, but footprints depend on product and boundary. Avoid generic sustainability claims without verified lifecycle data.
Pilot trials, batch testing, tight specifications and traceability protect quality when moving from lab to production.
Where Distil fits
Distil is a B2B specialty chemicals and polymer materials supplier serving plastics processors and OEMs. Its portfolio includes engineering plastics such as PA6 and PA66 from brands including LG Chem, with material-selection support for application requirements.
Availability of any specific grade should be confirmed directly with the team.
Conclusion: Selecting the Right Nylon Grade
PA6 and PA66 are closely related but not interchangeable. Match the grade to your priorities:
- PA6 for impact, flexibility, appearance and processing
- PA66 for higher heat, stiffness, load and wear
Decide through verified datasheets, application testing, processing trials and supply-chain evaluation, not family-level generalisations.
Frequently Asked Questions
Which is stronger, nylon 6 or nylon 66?
PA66 often offers higher stiffness, heat resistance and creep resistance. Reinforcement, moisture state, grade and test method can change the comparison, including which grade has the better impact result.
Is nylon 66 the same as nylon 6?
No. Both are polyamides, but PA6 comes from caprolactam and PA66 from adipic acid and hexamethylenediamine. Thermal, mechanical, moisture and processing behaviour differ.
What is nylon 66?
Nylon 66 is a polyamide made from adipic acid and hexamethylenediamine. It is common in demanding fibre and engineering-plastic uses such as airbags and under-bonnet parts.
What are the main uses of nylon 6?
Nylon 6 goes into textile and carpet yarn, packaging film, industrial yarn and tyre cord. It also makes engineering parts such as gears, bushings and electrical components.
How does moisture affect nylon 6 and nylon 66?
Absorbed water changes dimensions, stiffness, strength, creep, impact and electrical behaviour. For example, unfilled PA6 modulus falls from 3500 to 1200 MPa when conditioned. The effect varies with grade and humidity.
