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PA6/PA66 - properties, experiences and useful links

The members of the polyamide family are coded with cryptic extensions like 6, 11, 12, 66, 46 and 69. The numbers describe the type and number of polymer chains in their chemical structure. This approach, the normal practice in the industry, is not very user-friendly from the product designer’s perspective.

The two most commonly used polyamide grades by far are PA6 and PA66. The remaining members of the polyamide family are primarily used in applications that require unusually high service temperatures or tolerance of moist conditions. Bio-based and transparent (amorphous) PA grades are also available. In machine design purposes PA is often reinforced with glass or - in case of highly demanding applications - with carbon-fiber. Reinforcement changes the characteristics of the material and its applications considerably and therefore I’ll write a separate article on them later. This article focuses on unfilled PA6 and PA66.

What is the difference between PA6 and PA66 then?

Here is a summary:

PA66 compared to PA6

  • absorbs slightly less moisture
  • higher modulus
  • better wear resistance
  • better short term heat resistance

PA6 compared to PA66

  • better ductility (due to higher toughness)
  • better long term heat resistance
  • better impact resistance in low temperatures
  • better surface quality
  • better creep resistance
  • better UV-resistance (depends on modification)
  • lower cost

The differences are small, however, and in some circumstances some of the items on the list above may be invalid, depending on the exact grade in use.

For further information, the RTP-company provides good overviews of PA6 and PA66.

One of PA’s basic characteristics is its tendency to absorb water. This decreases its strength and modulus, but makes it tougher. More on PA water absorption can be read in Dry vs. Conditioned Polyamide Nylon Explained by UL-IDES

High gloss and good fatigue-, wear- and impact resistance makes PA a good option for plastic high end chairs.

Polyamide is commonly called nylon, which is also a trademark of Dupont. Here is a story about how nylon got its name.

Practical experiences of unfilled PA6/PA66:

  • Water absorption is a well-known property of PA and worth taking into account. The difference can be felt when a product that has been stored outdoors over winter is taken indoors for a few days: its stiffness invariably increases.
  • High quality cable ties are made of PA66. This illustrates well the strength and toughness of the material. It also reveals that unfilled PA is suitable for applications that require high flexibility or even integral hinge. Apart from cable ties, products made of unfilled PA66 are not very common. PA6 appears to be much more popular choice.
  • Because of its good surface appearance PA6 is also often used (rather than amorphous plastics ABS, PC, PC/ABS) on housings of some outdoor applications like this tractor. Read the full article on Basf site.
  • Even though parts made of PA can have a glossy surface, replacing amorphous grades like ABS with PA might cause problems because of the higher shrinkage and therefore warpage.
  • If you are trying to determine if a product is made of PA, cut a little piece off and burn it. The odor of PA is similar to burning hair.

I’ll add more links to the page every time I find something useful. If you have a good link, case or a story in mind, please email me at or add it in comments below.

To fully grasp the look and feel of PA you can order the Plasticprop Essentials sample kit including 20 of the most common plastics. It has been carefully designed to convey and explain the characteristics of each material. Read here what the sample tells about unfilled PA6.


I’m trying to replace my delrin part with another material. Would PA-66 be a suitable substitute?
Angel, It is hard to say without seeing the requirements, but usually PA-66 or PA-6 are common alternatives for POM and in many cases the the final material selection is done between these two materials. You have to be aware of the moisture absorption phenomenon with PA. Markus
Hello Markus Is there any chances to release the oil during the drying process of PA66 35%filled material
Vishal, I'm not sure if I got that right, but I don't see how it could happen. Markus
Dear Markus, I have a compound: By using DSC, I can know there is PA6 and PA66 inside. But: by using which method can I know the proportion of both material inside? Thanks in advance for your answer.
Hello Guillaumeme, I'm not sure if you can use DSC for that, and if you can, that goes beyond my experience. There are companies that are specialized on material analysis. Could you send a sample to one of these? Markus
Mb. Motaleb Mia, There is a big difference between short term use and long term use, especially if long term stress and elevated temperature come together. In such case I would be careful even far below 100°C. PA66 is slightly better but not significantly. Glass filling improves this. Data sheet values are easy to find with Google, but I recommend you do not blindly rely on those. Practical testing is always good. Markus
Pa6,pa66 can replace by any material with same properties??
Prabhu, PA is often replaced with PBT. But of course the properties are not exactly the same. Markus
prabhu praneeth
can pa410 can replce the pa66??
Prabhu, Do you mean the bio-based grade? I don't have practical experience on PA410, but my understanding is that from many perspectives this would be even an improvement. But most likely you'll have to accept higher cost. It is always good to test and compare. Markus
Ajith, I don't think it matters if you use PA6 or PA66 on the pin if it is the ABS part that is cracking. I'm not familiar with caproic acid and did not find it on my charts. Anyway, in general ABS is very poor when it comes to chemicals as PA is relatively resistant. Especially if there is some continuous stress involved, you should be in much better situation with PA. But it is worth testing. Elevated temperature should speed up the process so you can see the difference between these two material pairs. Good luck, Markus
Hi Markus (see I spelled your name correctly) We are moulding PA6 30GF FR. Single impression, single point of injection through a valve gate. We have issues with the fibres being visible on the surface. Mould temp is 90c (recommend 70-90c). Increasing the first stage fill rate helps considerably but even injecting at maximum speeds the issue is still visible. Additionally I understand that UV & FR additives are not compatible, do you have any suggestions? Note we must achieve V0 rating. Many thanks, Keith.
Keith, You probably understand the process parameters better than I do. I would have suggested increasing the mould temperature, but that you have done already. Perhaps going above the recommendation would make the difference? BR, Markus
Good Day Markus. I am dipping my toe into this Nylon industry and I don't know much. Can you speak on a PA 69 compared to a PA 6 and 66? I don't see much on a PA 69 and I was wondering why not?
Hi Markus! Very good article. A question: we are using the PA66-GF25/H as a roller cradle bearing cage, which was ultrasonically welded at two pins and serve as connection points. And we tensile tested the cage by ~350MPa, will the test weaken the connection? Can you recommend any NDT method suitable for internal defect detection for PA material? Thanks!
Arden, If that 350 MPa is close to the ultimate strength of the joint, I guess it could weaken it. But if you can stress the joint up to 700 MPa, or so, then probably not. Can you test it by pulling first to 350 MPa and then to failure. And as comparison straight to failure. If you do some 30 of each, you should see some tendency, if any. Markus
Hi Markus! The ultimate strength of the joint can be up to ~600MPa, no failure. So we have tested some (I don't have the number, may be 10+) on our product by ~350MPa, and ran them on endurance test rig, but many failed. We might want to understand if any (pre-existed) defect from material or resulted by previous tensile test.
Arden, Ultrasonic welding of semi-crystalline materials is a quite tricky process. You'll probably have relatively much variation on the end result. You'll need some statistical data to understand the process capability. If you test the ultimate strength of 30 samples, what is the variation? You can draw a rough Gauss curve based on the results. Markus


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