Material guide
Nylon 6 vs Nylon 6/6 (PA6 vs PA66): What's the Difference?
Nylon 6 and nylon 6/6 look the same and machine the same, but they differ in heat resistance, stiffness, moisture and how the stock is made. Here's how to choose, including where cast nylon fits.
Choose nylon 6/6 for slightly higher heat resistance, stiffness and strength in extruded rod and plate. Choose nylon 6 for better toughness and surface finish, and choose cast nylon 6 for large parts, low-stress machining and filled bearing grades. For most machined wear parts, the form (cast vs extruded) and filler matter more than 6 vs 6/6.
The short version
Nylon 6 (PA6) and nylon 6/6 (PA66) are both polyamides with nearly identical feel, color and machinability. Nylon 6/6 has a higher melting point and is a little stiffer and stronger. Nylon 6 is a little tougher and easier to process, and it's the base for cast nylon, which comes in much bigger sizes. Both absorb moisture, which affects every nylon part.
| Nylon 6 (PA6) | Nylon 6/6 (PA66) | |
|---|---|---|
| Melting point | ~428°F (220°C) | ~491°F (255°C) |
| Heat deflection / service temp | Good | Better |
| Tensile strength (dry) | ~11,000 psi | ~12,000 psi |
| Stiffness | Slightly lower | Slightly higher |
| Impact toughness | Slightly better | Good |
| Moisture absorption | Slightly higher | Slightly lower |
| Common stock forms | Cast nylon (very large sizes), extruded | Extruded rod, plate, tube |
| Relative cost | $–$$ | $$ |
Typical values for unfilled, dry-as-molded material. Nylon properties shift with moisture; confirm with the datasheet for your grade.
Heat and stiffness
Nylon 6/6's higher melting point gives it more margin in hot environments and a slightly higher heat deflection temperature, so it holds stiffness better near the top of its range. For parts running warm (engine compartments, hot conveyors, near ovens) or under steady load, 6/6 is the safer default. Heat-stabilized grades of either extend service life at elevated temperatures.
Moisture: true for both
All nylons absorb water from the air and swell slightly, which lowers stiffness and raises toughness. Nylon 6 absorbs a bit more than 6/6, but the difference is small next to the gap between nylon and acetal. If tight tolerances in humid or wet conditions matter, consider acetal or nylon 12. See Delrin vs nylon for that comparison.
Cast vs extruded: often the bigger decision
- Extruded nylon (often 6/6): standard rod, plate and tube in common sizes, consistent and widely stocked.
- Cast nylon 6: made in a mold, so it comes in very large diameters and thick plates. It has low internal stress (it stays flat and round when machined), higher crystallinity, and good wear.
- Filled cast nylons: MoS2 for wear (Nylatron GS-type grades), oil-filled for self-lubricating bearings, and heat-stabilized grades for warmer service.
Where nylon 12 and 11 fit
Nylon 12 and 11 absorb much less moisture and stay tough in the cold, at the cost of stiffness and heat resistance. They're common for tubing, fuel and air lines, and 3D-printed parts, and less common as machinable stock.
When to choose each
Choose nylon 6/6 for
- Warmer environments and steady loads
- Standard-size extruded rod and plate parts
- Slightly more stiffness and strength
- Electrical and automotive parts
Choose nylon 6 (cast) for
- Large sheaves, wheels, rollers and pads
- Low-stress machining of big parts
- Oil- or MoS2-filled bearing grades
- Impact and shock loads
Tip from the counter: when someone asks for "nylon" without a grade, ask about part size and environment. Big part or bearing duty points to cast nylon 6 with a filler; a small machined part near heat points to extruded 6/6.
Common questions
Which is stronger, nylon 6 or nylon 6/6?
Nylon 6/6 is slightly stronger and stiffer and holds up better at higher temperatures. Nylon 6 is a bit tougher under impact and has a better surface finish. Cast nylon 6, which is made differently from extruded nylon, often matches or beats extruded 6/6 in strength and wear because it's more crystalline and has less internal stress.
What is the difference between PA6 and PA66?
Chemistry and melting point. PA6 is made from a single building block (caprolactam) and melts around 428°F (220°C). PA66 is made from two (adipic acid and hexamethylenediamine) and melts around 491°F (255°C). That gives PA66 better heat resistance and stiffness; PA6 is easier to process and tougher.
Is nylon 6/6 more expensive than nylon 6?
Usually somewhat, at the resin level. In stock shapes, price depends more on the form: extruded rod and plate (often 6/6) versus cast nylon 6 (available in very large sizes), and on fillers like MoS2 or oil. Compare quotes for the size you need.
What is cast nylon?
Cast nylon is nylon 6 polymerized directly in a mold instead of being melted and extruded. It can be made in very large rods, tubes and plates, has low internal stress (so it machines stably), and is easy to modify with oil, MoS2 or heat stabilizers. It's the go-to for big sheaves, wheels, wear pads and bearings.
When should I use nylon 12 instead?
Nylon 12 (and nylon 11) absorb much less moisture than nylon 6 or 6/6, so they stay more dimensionally stable in wet or humid conditions, and they stay flexible and tough in the cold. They're common for tubing, fuel lines and 3D printing, but they're less stiff and less common as machinable stock shapes.
Values in this guide are typical figures for common unfilled grades, for general comparison only. Properties vary by manufacturer, grade, filler, and shape. Before you specify, buy or machine a material for an application, check the manufacturer's datasheet and the material certifications for the exact grade you're getting, and confirm suitability with your supplier.
Who stocks and machines it
Distributors that stock these materials and shops that machine or fabricate them, from the Stock & Shape directory.
Nylon
- Calsak Plastics – Minneapolis Blaine, MN
- Curbell Plastics – Hartford Windsor, CT
- Laird Plastics – Tampa Tampa, FL
- Piedmont Plastics – Salt Lake City Sandy, UT
- Arctic Manufacturing Services Anchorage, AK
- Grand Traverse Machine Co. Traverse City, MI
- Pilgrim Harp Avon Lake, OH
- Seastrom Mfg. Co. Twin Falls, ID