What are the main differences between PA 6.6 and PA 4.6 polymers?

In the nylon family, PA 6.6 and PA 4.6 are like two brothers, similar in appearance but with distinct personalities and capabilities. Both belong to the polyamide family, but they perform quite differently when dealing with high temperatures and high-stress applications.

Here are the main differences between them:

◾ High-Temperature Resistance

This is where the biggest difference lies.
PA 6.6: It's the most commonly used engineering plastic, handling general high-temperature environments without problems. However, in extremely hot engine compartments or high-temperature industrial equipment, it can sometimes struggle.
PA 4.6: It's a true "heat-resistant expert." Its molecular structure is more compact, allowing it to maintain its hardness at higher temperatures, unlike ordinary plastics that soften when heated. PA 4.6 can still function reliably in many extreme high-temperature conditions where even Polyamide 6 or PA 6.6 cannot withstand the heat.

◾ Strength and Rigidity

PA 6.6: It has well-balanced overall properties, offering good strength and durability, making it a preferred choice for many industrial parts.
PA 4.6: Its crystallization speed is very fast, meaning that parts made from it are harder and more rigid than those made from PA 6.6. If you need a part that won't deform at high temperatures, PA 4.6 is usually the better choice.

◾ Water Absorption

Nylon materials all share a common drawback – they absorb water.
PA 6.6: It has a moderate water absorption rate. After absorbing water, the parts will slightly expand and become a little softer.
PA 4.6: In comparison, PA 4.6 tends to absorb water faster and in larger quantities. This means that designers need to consider dimensional changes more carefully when using it in humid environments.

◾ Fatigue Life and Wear Resistance

PA 6.6: In everyday gears, switches, or housings, its wear resistance is already excellent, more durable than ordinary plastics.
PA 4.6: Under frequent friction and long-term stress, it has better "stamina." For example, in automotive applications such as timing chain guides or transmission parts, which undergo thousands of friction cycles, PA 4.6 typically has a longer lifespan and is less prone to wear than PA 6.6.

◾ Processing Characteristics

PA 6.6: Easy to process, with very mature technology; easily handled by most factories.
PA 4.6: Because it crystallizes quickly, the molding speed is also faster, which shortens the production cycle. However, due to its sensitivity to temperature, the machine settings during processing need to be more precise, requiring higher technical expertise from the factory.