What Is the Difference Between PA6 and PA66?

PA6 and PA66 are both aliphatic polyamides and form the most widely used group among engineering plastics. Their difference stems from molecular structure: PA6 is produced from a single monomer, PA66 from the combination of two different monomers.

This structural difference directly affects crystallisation behaviour and therefore thermal and mechanical performance.

PA66 has a markedly higher melting temperature than PA6. It is therefore preferred for parts continuously exposed to high temperature, such as under-the-hood components.

PA6, being processable at lower temperature, can offer advantages in energy consumption and cycle time.

Polyamides are hygroscopic; they absorb moisture from the air. PA6 absorbs more moisture than PA66. Moisture uptake increases part dimensions, reduces stiffness and increases toughness.

This is critical for tight-tolerance parts: a part straight out of the mould may not have the same dimensions as the same part a few weeks later. This must be accounted for in design and measurement processes.

Drying before processing is mandatory for both types; insufficient drying leads to surface defects and loss of mechanical strength.

PA6 has a wider processing window and generally gives better surface quality. PA66 can offer shorter cycle times thanks to fast crystallisation, but mould temperature control is more critical.

In engineering applications polyamides are mostly used glass fibre reinforced. Reinforcement markedly increases stiffness and heat deflection temperature while also reducing the dimensional effect of moisture uptake.

As fibre content rises, stiffness and strength increase while toughness and surface quality decrease. The right content is determined by the load and appearance expectations of the application.

If continuous high temperature and maximum mechanical strength are the priority, PA66 is usually more suitable; if cost, processability and surface quality lead, PA6 tends to fit better. In most projects the decision is made together with glass fibre content and flame retardancy requirements.

LG Chem's LUMID and LUXY families offer a wide grade selection in both polyamide types. Send us your application and we will identify suitable alternatives together.