Nylon 6 (polyamide 6, PA6) and nylon 66 (polyamide 66, PA66) are the two most common types of polyamides, 

and they have their own unique performance advantages. Toughness usually refers to the ability of a material to

resist fracture and not to break when impacted by external forces.

Nylon 6 (PA6) toughness is generally considered to be better than nylon 66 (PA66), especially in low temperature

environments. The molecular structure of PA6 causes it to be slightly more hygroscopic than PA66, which means 

that after hygroscopic, the toughness of PA6 is further improved because the presence of water makes the material 

more flexible. However, this also makes the dimensional stability of PA6 less than that of PA66 to a certain extent, 

which may not be suitable for some applications with strict size requirements.

Nylon 66 has better thermal stability, higher mechanical properties, and can maintain better strength and rigidity 

at higher temperatures. Although PA66 is somewhat less ductile than PA6, it is still a material with good toughness 

and is generally suitable for applications requiring high strength and dimensional stability.

When selecting the appropriate nylon material, environmental conditions, load conditions and cost factors for the 

specific application should be taken into account. Toughness requirements are not the only criteria for evaluating 

polyamide applications. Other performance indicators such as strength, rigidity, thermal stability, wear resistance, 

flame retardant and chemical resistance, etc., should also depend on the specific situation.

Of course, the toughness and wear resistance of PA6 or PA66 can also be increased by modification, and the 

additives to increase wear resistance can be referred to:What are nylon wear resistance additives?