Polyamide, commercially known as nylon, is one of the most widely used engineering polymers in industry.
In this guide, we examine the main types of polyamide (PA6, PA66, PA11, PA12 and filled grades) their key properties and the practical criteria for selecting the right grade.
Polyamide is a semicrystalline thermoplastic polymer characterised by the presence of amide groups (–CO–NH–) in the main chain. These groups give the material high mechanical strength, good toughness, wear resistance and chemical stability.
The most common polyamides are divided into two chemical families:
PA “AB”, obtained from a monomer that already contains both the amino group and the carboxylic group, such as PA6, PA11 and PA12;
PA “AABB”, obtained by polycondensation of a diamine and a dicarboxylic acid, such as PA66, PA46, PA610 and PA612.
The standard nomenclature is straightforward: the number indicates the number of carbon atoms in the monomer, so PA6 means 6 carbon atoms. In double-number grades, AABB, the first number indicates the carbon atoms in the diamine and the second those in the dicarboxylic acid. PA66 therefore means a six-carbon diamine plus a six-carbon dicarboxylic acid.
Polyamide offers an excellent balance between performance and cost:
high mechanical and fatigue strength for an unreinforced polymer;
wear resistance and a low coefficient of friction, making it suitable for moving parts;
good chemical resistance to oils, greases, hydrocarbons and many solvents;
continuous service temperature up to 80–100 °C for PA6/PA66, and above 150 °C for PA46;
good dry dimensional stability, although this is affected by moisture absorption.
There are dozens of polyamide grades available on the market, but five cover more than 90% of industrial applications.
Produced by polymerisation of caprolactam, PA6 is the most widely produced polyamide in Europe. Key characteristics:
melting temperature of approximately 220 °C;
excellent toughness and impact strength, even at low temperatures;
higher moisture absorption than PA66, up to 9–10% at saturation.
It is the preferred grade for bushes, moderately loaded gears, extruded semi-finished products such as rods and sheets, connectors and automotive components.
PA66 is a polymer produced from hexamethylenediamine and adipic acid. Compared with PA6, it has a higher melting temperature, around 260 °C, greater stiffness, better creep resistance and slightly better dimensional stability. Conversely, it is more expensive and less tough at low temperatures.
Typical applications include highly loaded gears, mechanical parts operating in hot environments, under-bonnet components, cable ties and technical fasteners.
PA11 and PA12 are produced from long-chain monomers, partly from bio-based sources. PA11 is derived from castor oil. Their distinctive characteristics are:
very low moisture absorption, around 1–2% at saturation compared with 9–10% for PA6, resulting in excellent dimensional stability;
excellent chemical and hydrolysis resistance;
high flexibility and fatigue strength, even at low temperatures.
They are the standard choice for flexible tubing in fuel and compressed-air circuits, coatings, under-bonnet automotive components, medical applications and additive manufacturing, including MJF.
For further detail, read our guide: PA12 vs. PA11: What Are the Differences?
PA46PA46 is a polyamide with high thermal performance, a melting temperature of approximately 295 °C and very rapid crystallisation. It is used for under-bonnet parts close to the engine, high-temperature gears and electrical components in hot environments. Its cost is significantly higher.
It should be noted that, despite its excellent high-temperature behaviour, PA46 is the most hygroscopic of the polyamides considered here. In very humid environments, the effect of water uptake must therefore be assessed.
The addition of mineral fillers or fibres can drastically modify the properties of the base polymer:
Unlike other engineering polymers such as POM, PEEK and PBT, polyamide is hygroscopic: it absorbs moisture from the environment, producing two opposing effects.
The positive effect is an increase in toughness and impact strength. A moisture-conditioned polyamide performs better under dynamic loads than a freshly moulded one.
The negative effect concerns dimensional stability and mechanical properties. Water acts as a plasticiser, reduces the elastic modulus and hardness, and causes the part to swell, up to 0.5–1% in linear dimensions for PA6.
For the design engineer, this means three things:
tolerances must be specified while taking the operating environment into account; PA6 in a saturated environment expands more than PA12 with the same geometry;
specifications must state whether the required properties refer to DAM (Dry As Moulded, i.e. dry polymer) or conditioned material (at equilibrium with 50% relative humidity); depending on the condition, the elastic modulus can vary by 30–50%;
surface finishes that seal surface microporosity and make the part water-repellent, such as vapor smoothing, should be considered. The surface becomes sealed against liquid water, while the bulk polymer remains hygroscopic with respect to atmospheric humidity.
|
Type |
Tm (°C) |
Rm (MPa) |
E modulus (GPa) |
H₂O Absorption (24h, %) |
Notes |
|
PA6 |
220 |
70–85 |
2.8–3.2 |
1.5–2 |
Tougher, lower cost |
|
PA66 |
260 |
80–90 |
3.0–3.3 |
1.2–1.5 |
Stiffer, more stable at temperature |
|
PA11 |
190 |
50–60 |
1.0–1.4 |
0.3 |
Bio-based, flexible, stable |
|
PA12 |
178 |
50–60 |
1.2–1.6 |
0.25 |
Excellent dimensional stability |
|
PA46 |
295 |
100 |
3.3 |
3.5 |
High-temperature applications |
|
PA6 GF30 |
220 |
170–180 |
9–10 |
1.3 |
Structural, low cost |
|
PA66 GF30 |
260 |
190–200 |
10–11 |
1.1 |
Structural, high temperature |
Indicative values for DAM (Dry As Molded) material. The absorption column reports the value after 24 hours of immersion and should not be confused with the saturation values cited in the text, which are significantly higher, for example 9–10% for PA6. Conditioned properties are significantly lower, especially for PA6 and PA66.
To identify the most suitable polyamide for a given application, the following factors must be assessed:
Selecting the wrong polyamide grade is one of the most costly mistakes in polymer component design. The problem is that it often does not appear immediately, but only after weeks or months of service: PA6 used in a very humid environment can absorb water, change dimensions and lose stiffness; PA66 replaced by PA6 in a gear can fail due to creep; a GF30 polyamide specified as “DAM” may show a much lower modulus under real operating conditions than expected, potentially falling by as much as half.
Polyamide is the most versatile engineering polymer in the industrial sector.
Selecting it correctly means starting from the design requirements and translating them into the right grade, with DAM or conditioned properties properly specified. When this is done, polyamide is one of the most reliable and efficient materials a design engineer can use.
Do you need to manufacture polyamide components with guaranteed properties?
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Yes. “Nylon” is the name under which DuPont introduced the material, which was synthesised in 1935 and named “nylon” in 1938. Contrary to common belief, it is not a registered trade mark: DuPont deliberately chose to make it a generic term. All thermoplastic polyamides are therefore “nylon”, and the actual grades (Nylon 6, Nylon 6/6 and Nylon 12) correspond exactly to the technical designations PA6, PA66 and PA12. In technical contexts and specifications, the “PA” designation with the numerical code is always preferred because it is unambiguous.
Yes. Polyamide is available as extruded or cast semi-finished stock, including round rods, sheets and tubes, and is well suited to turning, milling, drilling and cutting. It is best machined with sharp tools, high cutting speeds, controlled feed rates and careful management of heat build-up. Cast polyamides, such as PA6 G, have a more homogeneous structure than extruded grades and are preferred for precision parts.
Not in its standard form. Prolonged exposure to UV radiation degrades polyamide, causing yellowing, embrittlement and loss of properties. For outdoor applications, UV-stabilised grades or carbon-black-filled grades are used, as they offer significantly higher resistance.
Yes. Polyamides are thermoplastics and are therefore mechanically recyclable: they can be ground, remelted and reprocessed. However, recycling causes a progressive reduction in molecular weight and mechanical properties, so recycled material is typically used in blends with virgin material, or for less critical applications. Chemical recycling processes also exist, returning the polyamide to its original monomers.
PA6 and PA66 have similar but not identical properties. PA66 has a higher melting temperature, 260 °C compared with 220 °C, greater stiffness and better creep resistance, making it the preferred choice for applications under continuous load or at elevated temperatures. PA6 is tougher, absorbs slightly more moisture, offers a better surface finish and costs less. It is preferred where tough parts and complex injection-moulded geometries are required.
Long-chain polyamides PA11 and PA12 have the best dimensional stability thanks to their very low moisture absorption, 0.25–0.3% compared with 1.5–2% for PA6. They are the right choice where tolerances must be maintained even in humid or variable environments.
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