Nylon 6 or Nylon 66 - Which One Should I Choose?

Nylon 6 Nylon 66

Nylon (PA) 6 & 66 are both synthetic polymers called polyamides, with the numbers describing the type and quantity of polymer chains in their chemical structure. Most nylons, including 6 & 66, are semi-crystalline and possess good strength and durability for demanding applications.  

Nylon Properties

As polyamides, Nylon 6 & 66, whilst having their own separate and distinct benefits, do share many of the same core properties:

  • High mechanical strength, stiffness, hardness and toughness.
  • Good fatigue resistance.
  • High mechanical damping ability.
  • Good sliding properties.
  • Excellent wear resistance
  • Good electrical insulating properties
  • Good resistance to high energy radiation (gamma & x-ray).
  • Good machinability.

Differences

So whilst Nylon 6 & 66 are very similar materials, they do provide slightly different characteristics. The reason for the differences is largely due to their differences in chemical structure. Nylon 6 is made from one monomer which has 6 carbon atoms whilst Nylon 66 is made from 2 monomers with each one having 6 carbon atoms, hence the Nylon 66 name.

NYLON 6

NYLON 66

Less crystalline

More crystalline

Lower mold shrinkage

Exhibits greater mold shrinkage

Lower melting point

Higher melting point

Lower heat deflection temperature

Higher heat deflection temperature

Higher water absorption rate

Lower water absorption rate

Poor chemical resistance to acids

Better chemical resistance to acids

Withstands high impact and stress and better stands up to hydrocarbons

Better stiffness, tensile modulus and flexural modulus

Lustrous surface finish, easy to colour

More difficult to colour

 

An important difference between Nylon 6 & 66 is mold shrinkage. Nylon 6’s lower mold shrinkage adds reliability to final part dimensions which is beneficial whilst Nylon 66’s greater mold shrinkage, as it is exposed to cool air and solidifies, means the material’s shape changes more after processing, which must be accounted for.

Other key differences between the two nylons are water absorption rates and heat deflection temperatures. As Nylon 6 absorbs more water than Nylon 66 and has lower heat deflection temperatures, it is not suited to applications that are exposed to water at high temperatures. Nylon 66 would be a better choice between the two.    

Typical Material Applications

  • Sleeve and slide bearingsNylon 6 Nylon 66
  • Wear pads
  • Support and guide wheels
  • Cable sheaves
  • Hammer heads
  • Scrapers
  • Gear wheels
  • Seal rings
  • Cutting boards
  • Track plates

Which One Should I Choose?

The needs of an application have to be considered in terms of processing, aesthetic appearance, and mechanical properties first, in order to decide whether Nylon 6 or 66 is more suitable.

Nylon 6 should be used if a lightweight engineering plastic is required to withstand high impact and stress. It has better aesthetic appearance than Nylon 66 due to its lustrous finish and is easier to dye. It is an ideal choice for applications in the automotive, industrial and military industries. Common applications include: gears, firearm components and automotive engine compartments. It is not ideal, however, for applications that are exposed to water at high temperatures due to its higher water absorption and lower heat deflection rate than Nylon 66, which would be a better choice.

Nylon 66 should be used if a high performing engineering plastic is required that will be exposed to higher temperatures. Additionally, its stiffness and good tensile and flexural modulus make it an ideal material for applications that need repeated long-term performance. Typical applications include: friction bearings, radiator caps and tire ropes. 

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