Polyamide is one of the most widely used engineering plastics in industry – and for good reason. It combines high mechanical strength with good chemical resistance, a wide operating temperature range and ease of processing. It is used in automotive, electrical engineering, household appliances, construction and dozens of other industries, both in components exposed to dynamic loads and in precise details requiring dimensional stability.
This article is a complete overview of the properties of polyamide as a material class. Here you will find mechanical, thermal, chemical and electrical data, comparison tables and practical tips on what these numbers mean when designing components. The data refer primarily to the most popular technical varieties – PA6 and PA66.
For whom: engineers, designers, part designers, purchasing managers and technologists who select material for applications.
Mechanical properties
The mechanical properties of polyamide are strongly dependent on the variety of material and moisture content. All data below refer to the dry state after processing – the values for conditioned material (23°C, 50% relative humidity) are different and discussed in the hygroscopicity section.
Tensile strength
Technical polyamides achieve tensile strength in the range of 60–90 MPa. In practice, this means that they can carry significant static loads without permanent deformation – making them useful replacements for light metals in many applications that do not require extreme loads.
For comparison: structural steel reaches 250–400 MPa, aluminum about 200–300 MPa. Polyamide is not a substitute for metals in heavy-duty applications, but with the right cross-section and workpiece geometry, it is sufficient in a very wide range of applications – and much lighter.
Modulus of Elasticity (Stiffness)
| Material | Young’s Modulus (MPa) |
|---|---|
| Unmodified | 1,500–3,500 |
| Polyamide GF30 | 8,000-11,000 |
| Polyamide GF50 | 14,000–16,000 |
The addition of 30% fiberglass increases stiffness by three times or more – a key argument for using GF varieties wherever dimensional stability under load or creep resistance is required.
Impact strength
Polyamide exhibits good impact strength, especially in the conditioned state. The notched Charpy impact strength is 4–10 kJ/m² in the dry state and up to 15 kJ/m² in the conditioned state. At low temperatures, the material retains its useful impact strength down to approx. -30–40°C, making it the material of choice for applications exposed to impact in winter conditions.
Hardness and abrasion resistance
Shore Hardness D: 70–85 (depending on variety and moisture content). Polyamide has good abrasion resistance – better than PP or ABS, similar to POM. This justifies its use in gears, linear guides, plain bushings and friction-prone components.
Table: Mechanical properties of polyamide
| Property | Dry | Conditioned | Unit |
|---|---|---|---|
| Tensile | 60–90 | 45–70 | MPa |
| Young’s | 1,500–3,500 | 800–2,200 | MPa |
| Charpy impact strength (notched) | 4–10 | 8–15 | kJ/m² |
| Elongation at break | 20–50 | 100–300 | % |
| Shore Hardness D | 70–87 | 65–78 | – |
Thermal properties
Melting point and operating range
Engineering polyamides melt in the range of 215–265°C, depending on the variety. Approximate temperature range for continuous operation:
- Unmodified polyamide: -30°C to +100-120°C (short-term to +150-180°C)
- Polyamide GF30: -40°C to +140°C (briefly above +200°C)
“Polyamide retains 80% of its mechanical strength at 100°C, while many other plastics lose their properties as early as 60-70°C.”
Deflection Temperature Under Load (HDT)
HDT measured according to ISO 75 at 1.8 MPa:
- Unmodified polyamide: 60–90°C
- Polyamide GF30: 200-235°C
Fiberglass reinforcement raises HDT by more than 150°C – a major reason why GF varieties dominate in bonnet applications and other high-temperature environments.
Coefficient of Thermal Expansion (CTE)
Unmodified polyamide: approx. 80–90 × 10⁻⁶ K⁻¹. For GF30 varieties, the value drops to 25–40 × 10⁻⁶ K⁻¹ along the fiber. For comparison: steel – approx. 12 × 10⁻⁶ K⁻¹, aluminium – approx. 23 × 10⁻⁶ K⁻¹.
When designing metal-polyamide connections (e.g. metal inserts in polyamide housings), the difference in CTE must be taken into account – especially with large fluctuations in operating temperatures.
Creep
Unmodified polyamide has limited creep resistance at elevated temperatures – under constant load at 80°C, it deforms noticeably after several hundred hours. GF varieties exhibit significantly higher creep resistance, making them the material of choice for applications with permanent static loads.
Behavior at low temperatures
Polyamide retains its useful impact strength up to approx. −30–40°C. Below these temperatures, the material becomes brittle. For applications exposed to extremely low temperatures, it is worth considering impact modifiers or alternative plastics.
Chemical resistance
High resistance
Polyamides have good or very good resistance to:
- aliphatic and aromatic hydrocarbons (petrol, mineral oils, lubricants)
- alcohols (methanol, ethanol, isopropanol)
- alkaline and weakly alkaline solutions
- esters and ketones in moderate concentrations
- most organic solvents at room temperature
Low resistance
Avoid contact of polyamide with:
- strong mineral acids (sulphuric, nitric, hydrochloric acid in higher concentrations)
- strong oxidizers
- phenols and cresols
- glycerin at high temperature
Important: The chemical resistance of polyamide is highly temperature-dependent – a substance tolerated by PA6 at 23°C can cause degradation at 80°C. The concentration is similar: hydrochloric acid 5% is acceptable for polyamide in short-term contact, hydrochloric acid 30% causes rapid damage.
Chemical resistance table (selected substances)
| Substance | PA6 | PA66 | Remarks |
|---|---|---|---|
| Petrol | – | ||
| Engine | – | ||
| Hydraulic | – | ||
| Ethanol 96% | – | ||
| Isopropanol | – | ||
| Acetone | + | + | Temperature matters |
| Hydrochloric acid 10% | – | – | Degradation |
| Sulphuric acid 10% | – | – | Degradation |
| Acetic Acid 10% | + | + | Short-term contact |
| NaOH 10% | – | ||
| Distilled | + | PA6 swells | |
| Silicone | – | ||
| Glycerin | + | + | Sensitivity to temperature. |
| Phenol | – – | – – | Strong degradation |
Legend: ++ very good immunity, + good/moderate, – weak, – – no immunity
Electrical properties
Polyamide is an electrical insulator, which makes it useful in electrical engineering and electronics.
| Property | PA6 | PA66 | Unit |
|---|---|---|---|
| Cross-resistivity | 10¹³–10¹⁴ | 10¹³–10¹⁴ | Ω·cm |
| Electrical | 20–30 | 20–30 | kV/mm |
| Dielectric constant (1 MHz) | 3.5-4.0 | 3.5–4.5 | – |
| Loss Factor (1 MHz) | 0.02-0.03 | 0.02-0.04 | – |
The electrical properties of polyamide are sensitive to moisture – water absorption lowers resistivity and increases dielectric loss. In applications requiring stable electrical properties under varying humidity conditions, this should be taken into account or modified varieties with reduced hygroscopicity should be used.
Typical applications: connector housings, insulators, cable holders, relay and electronic component housings, plug-in connectors.
Hygroscopicity – a property you need to know
Polyamide absorbs moisture from the environment – and it is hygroscopicity that is the property that designers who do not know the specifics of this material most often forget.
Engineering polyamides can absorb up to 8-9% of their own water weight (equilibrium at 100% relative humidity). Under typical industrial conditions (50% relative humidity), the material is conditioned to approx. 2.5–3%.
“The absorption of 3% moisture by polyamide increases its impact strength by 50% – it’s a feature, not a bug.”
The effect of moisture on mechanical properties
| Property | Dry | Conditioned | Change |
|---|---|---|---|
| Tensile | 100% | ~70-80% | -20-30% |
| Young’s modulus (stiffness) | 100% | ~50-60% | -40-50% |
| Impact strength | 100% | ~150-200% | +50-100% |
| Elongation at break | 100% | ~300-500% | +200-400% |
Moisture plasticizes polyamide – it reduces stiffness and strength, but significantly improves impact strength and flexibility. For applications requiring vibration damping or impact resistance, conditioned PA6 is often the material of choice.
Dimensional consequences
Moisture absorption causes the material to swell – PA6 increases dimensions by approx. 0.5–1% when conditioned to 3% moisture. For components that work with metal inserts or require a precise fit, this must be taken into account in the design.
Moisture Management in Manufacturing
Before injection, the polyamide granules must be dried (80–100°C for 4–8 h). The material absorbed by moisture during injection molding causes hydrolytic degradation, blisters, surface defects and a decrease in the mechanical properties of the workpiece. Dried granules should be stored in an airtight container and used within a few hours of opening the package.
Wear and Friction Resistance
Polyamide has a good coefficient of friction and high abrasion resistance – especially when compared to non-engineering plastics such as PP or ABS. Under dry friction conditions, PA6 performs slightly better than PA66 due to its higher flexibility.
For applications requiring minimal friction, modified grades with the addition of MoS₂ (molybdenum disulfide) or PTFE are used, which reduce the coefficient of friction by 30-50% and improve resistance to abrasive wear.
Typical sliding applications: gears, linear guides, plain bushings, polymer bearings, cams, pins. Polyamide competes with POM here – POM has a slightly lower coefficient of friction in the dry state, but PA6 modified MoS₂ approaches these values at a lower cost.
Flammability and safety
Standard PA6 and PA66 are classified as HB (horizontal burn) according to UL94 – which means slow horizontal burning without spontaneous extinguishing. For applications in electronics, electrical engineering and construction, higher flammability classes are often required.
Flame retardant (FR) modifications allow you to achieve classes V0, V1 or V2. The most commonly used FR systems are halogen (effective but with environmental limitations) and halogen-free (required in a growing number of specifications). The auto-ignition temperature of PA6 is approx. 450–500°C.
Modifications and Reinforcements
Unmodified PA6/PA66 is the starting point – in industrial practice, modified varieties dominate:
- PA6/PA66 + GF (Fiberglass, 15-50%) – doubles or triples strength and rigidity, greatly improves HDT and creep resistance, lowers shrinkage and improves dimensional stability. The cost is higher brittleness and abrasiveness (accelerated mold wear).
- PA6/PA66 + mineral fillers – talc, chalk, kaolin reduce the cost of the material, improve stiffness and reduce shrinkage, but reduce impact strength and tensile strength.
- Impact modifiers – elastomers (EPDM, EPR) added to PA improve impact strength even several times, at the expense of lower stiffness. Used in bumpers and impact-prone housings.
- UV stabilizers – standard PA degrades under the influence of UV radiation (yellowing, brittleness). UV stabilizers (e.g. HALS) are necessary for outdoor applications.
- Flame retardants (FR) – enable the achievement of flammability classes V0–V2 according to UL94 for applications in electrical and electronics.
Comparison of polyamide with other plastics
| Property | PA6/PA66 | POM | PC | |
|---|---|---|---|---|
| Tensile | 70-90 MPa | 60-70 MPa | 25-40 MPa | 55-70 MPa |
| Continuous | up to 120°C | up to 100°C | up to 100°C | up to 120°C |
| Chemical | good | good | very good | moderate |
| Friction/abrasion | Good | very good | moderate | Weak |
| Hygroscopicity | high | very low | very low | Low |
| Relative | Average | medium-high | Low | high |
- PA vs POM: POM has a lower coefficient of friction and is more dimensionally stable. PA6 is cheaper and better in impact applications. POM does not tolerate acids, PA6 does not tolerate bases – everyone has their own chemical niche.
- PA vs PP: PP is much cheaper and has very good chemical resistance, but much lower strength and rigidity. PP is used where lower mechanical properties are sufficient; PA6 – where true technical strength is required.
- PA vs PC: PC has better transparency and impact strength at low temperatures, but it is more expensive and more sensitive to ketones and esters. PA6 GF30 wins over PC in high-temperature applications.
FAQ – frequently asked questions
What is the maximum operating temperature of polyamide?
For non-modified PA6: approx. 100°C continuous, short-term up to 150°C. For PA66: approx. 120°C continuous, short-term up to 180°C. GF-reinforced varieties have an HDT of 200–235°C, but the long-term operating temperature is limited by thermal oxidation – for heat-stabilized PA66 GF, approx. 150–160°C is assumed as the maximum for long-term use.
Is polyamide suitable for contact with food?
Standard PA6 and PA66 can be used in contact with food provided it meets regulatory requirements (e.g. EU Regulation 10/2011). It is crucial to use the right components and obtain a declaration of conformity from the supplier of the granules. Not every commercial grade is intended to come into contact with food – this should be checked in the technical data sheet.
How does moisture affect the mechanical properties of polyamide?
Absorption of 2.5–3% moisture reduces tensile strength by approx. 20–30% and Young’s modulus by approx. 40–50%, but increases impact strength by 50–100% and elongation at break several times. The design of polyamide components should be based on conditioned properties, not dry properties – because it is the conditioned state that corresponds to the actual operating conditions.
Is polyamide resistant to gasoline and oils?
Yes – the resistance of PA6 and PA66 to hydrocarbons (petrol, mineral oils, lubricants) is good and is one of the key advantages of these materials in the automotive industry. Resistance is better at low temperature; At elevated temperatures, it is worth conducting tests with a specific medium.
What is the difference between PA6 and PA66?
PA66 has higher operating temperature and rigidity, PA6 is cheaper and more impactful. For a detailed breakdown with tables and a case study, see PA6 vs PA66: A Complete Guide to the Differences.
Is polyamide an eco-friendly material?
Standard PA6/PA66 is derived from petrochemical raw materials and is not biodegradable. At the same time, its high strength allows for the design of lighter components (lower material consumption), and its thermoplastic nature allows for recycling. Biobased varieties of PA (e.g. castor oil PA11) are available, but they have different properties and a higher cost. Post-production recycling of polyamide is technically possible and practiced in many plants.
Summary
Polyamide is a versatile engineering material that deservedly ranks at the forefront of engineering materials. High mechanical strength, good chemical resistance to hydrocarbons and alkalis, a wide range of operating temperatures and the possibility of modification (GF, MoS₂, FR) make polyamide the material of choice in dozens of applications.
A key rule when designing with polyamide: always consider hygroscopicity. Design for conditioned properties, not dry properties – because it is the conditioned material that works in your component.
Need help choosing a material? Contact our technical department – we advise at the design stage and select the grade according to the requirements of the application.