Are you planning to order a plastic workpiece and don’t know if PA6 is enough or do you need PA66? This is one of the most common questions that designers and technologists from production plants, companies from the automotive and energy industries come to us with.
The answer is not always obvious – both materials belong to the polyamide family, but have clearly different mechanical, thermal and economic properties. This article explains the differences in a way that is useful for making a design decision, not just theory. We rely on 35 years of experience in the production of plastic components and order fulfillment for customers in 49 countries.
Who is this article for: for designers, technologists, buyers and production managers who order or design plastic components and need a solid basis for material selection.
What is PA6 and PA66?
Both materials are thermoplastic polyamides – synthetic plastics with very good mechanical properties, commonly used in industry as a substitute for metals in structural elements, guides, pins, bushings, gaskets and hundreds of other applications.
PA6 (polyamide 6, nylon 6) is formed by the polymerization process of caprolactam. Its main features are good impact strength, ease of processing and lower raw material price. In Poland and Europe, it is one of the most popular varieties of polyamide used in industry.
PA66 (polyamide 6.6, nylon 6.6) is made from two monomers: hexamethylenediamine and adipic acid. The polymer chain is more regular, which translates into a higher melting point, higher rigidity, and better creep resistance under load.
Both materials can be reinforced with glass fiber (e.g. PA6 GF30, PA66 GF30), filled with MoS₂, PTFE or other modifiers – and it is the reinforced varieties that dominate in technical applications.
Comparison Table of PA6 and PA66 Properties
Below is a summary of key parameters for unmodified PA6 and PA66 varieties according to standard processor data:
| Property | PA6 | PA66 | Unit |
|---|---|---|---|
| Melting | ~220°C | ~260°C | °C |
| Deflection Temperature Under Load (HDT, 1.8MPa) | 60–70°C | 70-90°C | °C |
| Tensile | 70-80 MPa | 80-90 MPa | MPa |
| Young’s modulus (stiffness) | 2800–3200 MPa | 3000-3500 MPa | MPa |
| Charpy impact strength (notched) | 4–6 kJ/m² | 4–5 kJ/m² | kJ/m² |
| Absorbency (equivalent) | 2.7-3.5% | 2.5–3.0% | % |
| Processing | 1.0-1.5% | 1.0-1.5% | % |
| Chemical Resistance (General) | good | good | – |
| Ease of processing | very good | good | – |
| Relative price of raw | lower | higher (~20-40%) | – |
Note: Values may vary depending on the pellet manufacturer, humidity and processing conditions. The data for ISO 1110 conditioned plastics may be significantly different than for the dry state.
When to use PA6 and when to use PA66?
Choose PA6 if:
- The operating temperature is moderate – up to approx. 100–110°C under continuous conditions, without short-term spikes above 180°C.
- You care about impact strength – PA6 is a bit more “ductile” and better absorbs impact in applications such as guides, pins, polymer bushings.
- Price matters – with large batches, the difference in the price of the raw material between PA6 and PA66 adds up to real savings.
- The geometry of the workpiece is complex – the lower viscosity of the PA6 alloy makes it easier to fill thin ribs.
- The component is not exposed to prolonged static loads at elevated temperatures.
Choose PA66 if:
- The operating temperature exceeds 110°C – e.g. components under the bonnet, housings near the exhaust or heating system.
- The component works under constant mechanical load – PA66 has better creep resistance and stress relaxation.
- Higher rigidity is required – brackets, beams, structural elements.
- The working environment is chemically aggressive – PA66 has slightly better resistance to oils and fuels at higher temperatures.
- A technical specification or OEM standard requires PA66 directly (e.g. IATF 16949 or Tier 1 specifications).
Practical principle: If you don’t have detailed temperature requirements or large constant loads – PA6 is a safe default choice and less expensive. If the operating parameters are demanding or you don’t know the exact working environment, PA66 gives you a safety margin.
“The choice between PA6 and PA66 is not a question of quality – it is a matter of matching the material properties to the operating conditions of the component.”
Price and availability differences
In market practice (indicative data from 2025-2026), PA66 granules are 20-40% more expensive than PA6, depending on the variety, manufacturer and order quantity. Reinforced varieties (GF30, GF50) have a narrowed price spread, because the cost of fiberglass dominates the price structure.
PA6 is widely available from all major granule manufacturers (BASF, DSM, Lanxess, Toray, Radici) and many processors have it in stock at all times, which facilitates short lead times.
PA66 has been a material with limited availability in recent years – especially in 2021-2022, the market experienced global shortages of adipic acid after failures of production plants. It is worth taking this into account when designing critical components and considering material inventory planning or replacement certification.
“With large production runs, the difference in the price of raw material between PA6 and PA66 can account for 20-40% of the cost of the material – an argument that is always worth analysing at the material selection stage.”
Case study: replacement of PA6 with PA66 in an automotive component
Background: An automotive component manufacturer reported a deformation issue with the cable harness guide bracket in the engine compartment, made of PA6 GF30. The component operated at an ambient temperature of 120–130°C under constant tension from the clamp.
The problem: after 6-12 months of operation, there was marked deformation – the material was creeping and the mounting angles were out of tolerance, causing the beam to be frictional.
The solution: change the material to PA66 GF30 without modifying the geometry of the workpiece or the tool – the injection mold remained the same because both materials have identical processing shrinkage.
Effects after changing the material:
- HDT increased from approx. 200°C (PA6 GF30) to ~235°C (PA66 GF30) according to ISO 75 at 1.8 MPa.
- Creep at 130°C after 1000 h: residual deformation reduced by approx. 60%.
- Complaints about assembly at the customer: decrease from 3.2% to less than 0.2% in the first year after the switch.
- Increase in material cost per part: +28% (PA66 GF30 vs PA6 GF30 in this application).
Conclusion: the cost of changing the material was many times lower than the cost of complaints and downtime. The change was possible without redesigning the mold – a key advantage when the tool is ready and time is limited.
FAQ – frequently asked questions about PA6 and PA66
Can PA6 and PA66 be produced on the same injection mold?
In most cases, yes – the processing shrinkage of both materials is approx. 1.0–1.5% for varieties without filling and a similar value for varieties with GF. The differences are small enough that changing the material between PA6 and PA66 rarely requires tool modification. However, it is worth consulting the critical dimensions with the technologist, especially with tight tolerances.
Which polyamide tolerates contact with water and moisture better?
Both materials absorb moisture – this is a characteristic feature of polyamides. PA6 absorbs slightly more (approx. 2.7–3.5% at steady state) than PA66 (approx. 2.5–3.0%). It is crucial to design with the conditioned state in mind, not the dry state after processing – the mechanical properties of wet PA6 and PA66 differ significantly from the data from the data sheets.
Is PA66 always better than PA6?
No. PA66 is better where higher operating temperature and rigidity are important. In impact applications, on tight budgets, or when temperatures do not exceed 100°C, PA6 can be the optimal choice. The choice of material should be based on the requirements of the application, not the belief that “better material = higher number”.
How quickly can you start production with PA6 or PA66?
It depends on the availability of the tool (injection mold) and the raw material. If the mold is ready and the material is in stock, the time from order to start production can be several hours. For new designs, the mold execution time is the dominant factor.
Are other polyamides available for demanding applications?
Yes – when PA66 is not enough, the next step is PA46, PA6T, PA66/6T or partially aromatic polyamides (PPA). They have higher operating temperatures (above 180–200°C continuous), but are much more expensive and require higher processing temperatures. It is worth considering them when the application specification clearly exceeds the capabilities of the PA66.
Summary
PA6 and PA66 are the two most popular technical polyamides – they differ mainly in operating temperature, stiffness and price. PA6 is suitable for applications with moderate thermal requirements, PA66 is the choice for components operating at higher temperatures and under constant load.
It is worth consulting the choice of material with the supplier of the parts – especially if you have a ready-made mould and want to assess whether a change in material is possible without modifying the tool.