PA6 and PA66 are the two most widely used nylons. Their names differ by just one "6" and they look almost identical, yet each has its own strengths in heat resistance, moisture absorption, processing and price. Choose the wrong one and you may get deformed parts at best, or a whole batch of rework at worst. Below we compare them on five points.
1. Heat resistance: PA66 is higher
PA66 has a melting point of about 260℃, PA6 about 220℃. With glass fiber added, the heat deflection temperature of both rises sharply, but PA66 usually stays a notch higher. For parts exposed to high temperatures over the long term, such as components around the engine compartment or near heat-generating areas of electrical appliances, PA66 is generally the first choice.
2. Stiffness and toughness: PA66 is stiffer, PA6 is tougher
Under the same conditions, PA66 offers slightly higher strength and stiffness, while PA6 usually provides better toughness, impact resistance and surface gloss. For structures with snap fits that are assembled repeatedly or that must not crack when dropped, PA6 or impact-modified PA6 is often the better fit.
3. Moisture absorption: both absorb water, PA6 slightly more
Nylon absorbs moisture from the air. After absorbing water the material becomes tougher, but strength and stiffness drop and dimensions grow slightly. Generally speaking, PA6 has a somewhat higher water absorption than PA66. For parts with tight dimensional tolerances, the changes caused by moisture absorption should be factored into the design in advance, or glass-fiber-reinforced or mineral-filled compounds should be used to reduce the effect.
4. Processing: PA6 has a wider window
PA6 has a lower melting point and a wider processing temperature window, places relatively looser demands on molds and equipment, and makes it easier to achieve a good surface on cosmetic parts. PA66 crystallizes quickly and has short molding cycles, making it suitable for high-volume production, but it requires tighter temperature control.
5. Cost: PA66 is usually more expensive
In most cases PA66 resin is priced higher than PA6, and the exact price gap fluctuates with the raw material market. If PA6 already meets the performance requirements, choosing PA6 can significantly reduce material cost.
A simple selection guide
1. Long-term high temperature and high stiffness required: go for PA66 or glass-filled PA66 first.
2. Toughness, appearance and cost sensitivity: go for PA6 or impact-modified PA6 first.
3. Flame retardancy required: flame-retardant compounds are available for both; then choose between them based on heat resistance and cost.
4. When in doubt: put together the service temperature, load conditions, wall thickness and certification requirements, then validate with sample parts.
RJF Plastics supplies both PA6 and PA66 resins and a wide range of modified compounds, and can recommend materials based on your part. The above is general information; actual properties are subject to the material's datasheet.