PA6 vs PA66: Properties, Injection Molding Differences, and Material Selection

Choosing between PA6 vs PA66 is not simply a question of which nylon is stronger. PA66 generally offers higher stiffness and better thermal performance, while PA6 is usually tougher, easier to process, and less expensive. For injection-molded OEM parts, HingTung looks beyond the polymer name. Temperature, load, humidity, tolerance, glass-fiber content, geometry, and molding conditions all influence which grade will perform better in the finished part.

PA6 vs PA66 at a Glance

PA6 is also called Nylon 6 or Polyamide 6. PA66 is commonly known as Nylon 66, Nylon 6/6, or Polyamide 66. The table below gives useful reference values for a basic PA6 vs PA66 comparison.

Property	PA6	PA66
Density	~1.13–1.14 g/cm³	~1.14–1.15 g/cm³
Melting point	~220–223°C	~255–260°C
Typical melt processing range	~240–270°C	~270–300°C
Elastic modulus, reference example	~3.3 GPa	~3.5 GPa
Long-term service temperature, example grade	~100°C	~100°C
Short-term service temperature, example grade	~160°C	~170°C
Moisture absorption	Generally higher	Generally lower
Impact toughness	Generally higher	Lower
Relative raw material cost	Generally lower	Generally higher

The mechanical and service-temperature figures above are useful reference points, not universal PA specifications. For example, Ensinger lists elastic moduli of about 3,300 MPa for one PA6 grade and 3,500 MPa for one PA66 grade, with short-term service temperatures of approximately 160°C and 170°C respectively. The actual difference may become much larger once glass fiber, heat stabilization, flame retardants, or other additives are introduced.

What Is the Difference Between PA6 and PA66?

The difference starts with their molecular structure.

PA6 is produced from caprolactam.
PA66 is produced from hexamethylenediamine and adipic acid.

PA66’s more regular structure contributes to a higher melting point and generally higher stiffness. PA6 tends to provide more toughness and a more forgiving processing window. For molded parts, those chemical differences show up in practical areas such as crystallization, moisture uptake, shrinkage, processing temperature, and dimensional behavior. That is why PA66 vs PA6 should be judged against the actual application instead of treating PA66 as automatically superior.

PA6 vs PA66 Mechanical Properties

For comparable unfilled grades under similar test conditions, PA66 normally has slightly higher stiffness and tensile performance. PA6 is generally tougher and more tolerant of impact or deflection. A useful reference comparison is:

Mechanical Factor	PA6	PA66
Elastic modulus, one reference family	~3,300 MPa	~3,500 MPa
Stiffness	Moderate-high	Higher
Impact behavior	Generally better	More rigid
Load-bearing performance	Good	Generally better
Effect of moisture	Significant	Significant, usually somewhat lower

These differences are often smaller than people expect. Reinforcement can matter much more than the difference between the base polymers. For example, a PA6-GF30 grade may easily provide greater stiffness than an unfilled PA66. So PA6 vs PA66 mechanical properties should be compared at the actual grade level. Moisture condition matters as well. A dry-as-molded nylon part is usually stiffer, while a conditioned part may become tougher and more flexible. Datasheet values should therefore only be compared when the testing and conditioning conditions are similar.

PA6 vs PA66 Heat Resistance

The clearest thermal difference is melting point.

PA6: approximately 220–223°C
PA66: approximately 255–260°C

But melting temperature should not be confused with usable service temperature. A PA6 reference grade from Ensinger, for example, lists a glass transition temperature of 45°C, melting temperature of 221°C, long-term service temperature of 100°C, and short-term service temperature of 160°C. Those four numbers describe very different things.

Thermal Value	What It Means
Tg	Change in amorphous-phase mobility
Melting point	Melting of crystalline regions
HDT	Deformation under a specified load
Service temperature	Practical temperature capability over time

This is especially important when checking the HDT of PA6 vs PA66. A nylon component does not suddenly become unusable above Tg because PA6 and PA66 are semi-crystalline materials. For load-bearing parts exposed to heat, HDT, load, exposure time, reinforcement, and mechanical-property retention are more useful than melting point alone.

Moisture Absorption and Dimensional Stability

PA6 vs PA66 Moisture Absorption Dimensional Stability

Moisture is one of the most important differences to consider when molding nylon. Both materials are hygroscopic, but PA6 generally takes up more moisture than PA66. The exact percentage depends heavily on the grade and test method. For example, one unfilled PA6 reference grade lists water absorption of approximately 0.3% after 24 hours and 0.6% after 96 hours at 23°C under ISO 62. Longer-term or equilibrium moisture values can be much higher, which is why a percentage should never be quoted without its test condition. Moisture can change:

dimensions
stiffness
impact toughness
assembly fit
long-term tolerance stability

Thermal expansion adds another source of dimensional change. The same PA6 reference grade lists a CLTE of approximately 12 × 10⁻⁵/K from 23–60°C and 13 × 10⁻⁵/K from 23–100°C. This is why critical nylon dimensions should have a defined measurement condition. A part measured immediately after molding may not have exactly the same dimensions after moisture conditioning or temperature exposure. Our guide to moisture absorption in PA injection molding covers this effect in more detail. For projects with tight fits or mating dimensions, HingTung considers expected humidity and conditioning during DFM rather than checking tolerance only on freshly molded samples.

PA6 vs PA66 Injection Molding Differences

PA6 normally processes at lower temperatures and tends to provide a wider process window. PA66 requires higher melt temperatures and closer thermal control. Typical published processing ranges are:

Processing Reference	PA6	PA66
Melting point	~220–223°C	~255–260°C
Typical melt range	~240–270°C	~270–300°C
Drying before molding	Required	Required
Shrinkage	Grade-dependent	Grade-dependent

Drying is particularly important. Moisture that remains in the resin can cause hydrolytic degradation when the polymer is heated, reducing molecular weight and potentially weakening the finished part. Shrinkage is harder to reduce to one number. The actual shrinkage PA6 vs PA66 relationship changes with:

glass-fiber percentage
flow direction
wall thickness
mold temperature
packing
gate position
cooling conditions

Glass-filled grades generally shrink less overall, but fiber orientation makes shrinkage more directional. That can increase warpage in injection-molded parts around ribs, bosses, corners, and long flow paths. For tooling, the nominated grade’s shrinkage data is more useful than a generic PA6 or PA66 percentage.

How Glass Fiber Changes PA6 vs PA66

For many structural components, the real comparison is PA6-GF30 versus PA66-GF30, not unfilled PA6 versus unfilled PA66. Glass fiber generally improves:

stiffness and strength
HDT
dimensional stability
creep resistance
overall shrinkage control

But it also introduces anisotropy and additional tool wear.

Material	Typical Position
Unfilled PA6	Tough, easier to process
PA6-GF30	Stronger and stiffer with lower overall shrinkage
Unfilled PA66	Higher thermal and stiffness baseline
PA66-GF30	High stiffness and strong elevated-temperature performance

Our guide to glass-filled vs unfilled PA injection molding explains these trade-offs in more detail. Because glass fiber is abrasive, reinforced nylon can also accelerate injection mold wear at gates, runners, and other high-shear locations. For higher-volume programs, tool steel and maintenance planning should therefore be considered together with material selection.

PA6 vs PA66 Cost

A basic PA6 vs PA66 cost comparison usually favors PA6, but a fixed percentage difference is not reliable. Material prices change with region, supplier, grade, glass-fiber content, flame retardants, heat stabilizers, color, and purchasing volume. For context, published PA6 market references for Q2 2026 reached approximately:

Market	PA6 Reference Price
China	US$1,680/MT
Germany	US$2,120/MT
USA	US$3,132/MT

These are market indicators rather than quotations for a specific injection-molding grade. The market can also move differently for PA6 and PA66. In April 2026, Celanese announced Asian price increases of US$0.30/kg for specified non-flame-retardant PA6 products and US$0.50/kg for specified PA66 products, illustrating why a permanent “PA66 costs X% more” rule is unreliable. For OEM production, resin price per kilogram is only one part of the decision. Scrap rate, process stability, conditioning, cycle performance, mold wear, and product life all affect the cost of an acceptable finished part.

Which Should You Choose: PA6 or PA66?

There is no universal winner. Start with the actual operating conditions.

Requirement	Usually Evaluate First
Better impact toughness	PA6
Lower raw material cost	PA6
Easier processing	PA6
Higher stiffness	PA66
Higher thermal requirement	PA66
Lower moisture uptake	PA66
High structural performance	GF-reinforced PA6 or PA66
Tight dimensional control	Compare specific grades and conditioning data

Material should ideally be finalized before tooling. Moving from unfilled PA6 to PA66-GF30 can change shrinkage, gate design, processing temperature, warpage behavior, and tool-wear requirements. HingTung combines injection molding material selection with DFM, mold manufacturing, trials, and production validation so the selected grade is evaluated against the real part rather than chosen from one datasheet number.

FAQ

Is PA66 the same as Nylon 66?

Yes. PA66, Polyamide 66, Nylon 66, Nylon 6,6, and Nylon 6/6 are commonly used names for the same polymer family.

Can PA6 and PA66 be identified visually?

Not reliably. Colorants, glass fiber, fillers, and other additives can make different nylon grades look very similar. Material certification or appropriate identification testing is more reliable.

Can PA6 and PA66 be mixed during molding?

Uncontrolled mixing is not recommended. Their melting and crystallization behavior differs, so contamination can affect processing stability and final part properties.

Can recycled PA6 or PA66 be used for structural parts?

It can be suitable for some applications, but recycled resin may introduce additional variation in viscosity, contamination, moisture history, and mechanical performance. The acceptable recycled content should be validated against the actual part requirements.

Conclusion

The practical PA6 vs PA66 decision depends on more than strength or price. PA6 usually offers a good balance of toughness, processability, and cost, while PA66 is often preferred when stiffness and elevated-temperature performance become more demanding. For OEM molded parts, HingTung evaluates the specific material grade together with moisture, geometry, tooling, tolerance, and production conditions so the choice works in actual molding and long-term use, not only on the datasheet.

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