PA6 PA66 PA12 PA1010 Nylon Injection Molding Process

PA6, PA66, PA12, and PA1010 are the four most commonly injection-molded nylon grades, each with distinct moisture absorption, temperature resistance, and mechanical properties that make them suited to different applications. Choosing the wrong grade leads to dimensional instability, brittle failure, or unnecessary cost. This guide compares all four grades side by side so you can specify the right material for your injection molding project.

What Are PA6, PA66, PA12, and PA1010 Nylon Grades?

Polyamide (nylon) is a semi-crystalline engineering thermoplastic characterized by strong hydrogen bonding between amide groups in adjacent polymer chains. This intermolecular bonding gives nylon its trademark combination of high strength, toughness, and abrasion resistance. The number in each grade name indicates the carbon atom count in the monomer, which directly affects crystallinity, melting point, and moisture absorption behavior.

Comparing PA6 vs PA66: Moisture and Strength Trade-offs

>PA6 (polyamide 6) is produced by ring-opening polymerization of caprolactam, a six-carbon monomer. It melts at approximately 220°C and offers good mechanical properties at moderate cost. PA6 crystallizes at a slower rate than PA66, which gives slightly longer cycle times but reduces warpage risk in complex geometries. PA6 is the most widely molded nylon grade globally by volume, used in everything from cable ties to automotive intake manifolds.

PA66 (polyamide 6,6) is produced by polycondensation of hexamethylenediamine and adipic acid, both six-carbon monomers. The symmetrical molecular structure produces higher crystallinity and a higher melting point of approximately 260°C. PA66 is approximately 15 to 20 percent stiffer than PA6 at room temperature and retains mechanical properties at elevated temperatures better than any unfilled nylon grade. This makes PA66 the standard choice for under-hood automotive components and electrical connectors operating above 120°C.

PA12 and PA1010: Bio-Based, Long-Chain Polyamides

>PA12 (polyamide 12) is produced from laurolactam, a twelve-carbon monomer. The longer aliphatic chain reduces the density of amide groups along the polymer backbone, which dramatically lowers moisture absorption to approximately 0.25 percent compared to 2.5 to 3.0 percent for PA6. PA12 melts at approximately 178°C, processes easily, and delivers excellent dimensional stability in humid environments. It commands a significant price premium over PA6 and PA66, typically 3 to 5 times higher per kilogram.

PA1010 (polyamide 10,10) is produced from sebacic acid and decamethylenediamine, both derived from castor oil. This renewable feedstock origin makes PA1010 attractive for applications requiring bio-based content certification. PA1010 combines low moisture absorption (approximately 1.0 to 1.5 percent) with good chemical resistance and flexibility, positioning it between PA12 and PA6 in both performance and cost. It is gaining adoption in automotive fuel lines and hydraulic tubing where renewable content is specified.

What Are the Key Property Differences Between PA6, PA66, PA12, and PA1010?

The four nylon grades differ most significantly in moisture absorption, melting point, stiffness, and chemical resistance. These differences are not subtle — selecting the wrong grade can double your part’s dimensional variation or halve its service temperature. The table below provides the engineering data needed for material selection.

Moisture absorption is the single most important differentiator for processing and application design. PA6 and PA66 absorb 2.5 to 3.0 percent moisture at equilibrium in a 50 percent relative humidity environment, which causes dimensional swelling of 0.5 to 1.0 percent and reduces stiffness by 50 to 60 percent compared to the dry-as-molded state. PA12 absorbs only 0.25 percent, making its dimensional change negligible. If your application requires tight tolerances in a humid environment, PA12 is the clear choice regardless of its higher raw material cost.

The notched Izod impact values marked NB (no break) for PA12 and PA1010 indicate that these grades are inherently tough and do not exhibit brittle fracture in standard impact tests. This toughness, combined with low moisture absorption, makes PA12 and PA1010 the preferred choices for fuel lines, hydraulic tubing, and pneumatic fittings where impact resistance must be maintained across temperature and humidity ranges.

What Are the Critical Processing Parameters for Each Nylon Grade?

Nylon molding parameters are more demanding than commodity plastics like PP or PE because of the material’s high melting temperature, narrow processing window, and sensitivity to moisture. Getting drying and melt temperature wrong is the most common cause of defective nylon parts in production.

Drying requirements vary significantly across the four grades. PA6 and PA66 require 4 to 8 hours at 80 to 100°C in a dehumidifying hopper dryer to reach below 0.2 percent moisture. PA12 needs only 2 to 4 hours at 70 to 80°C due to its low moisture absorption. PA1010 falls between at 3 to 6 hours at 80 to 90°C. All four grades should be dried immediately before molding — leaving dried pellets exposed to ambient air for more than 30 minutes negates the drying effort.

Melt temperature settings follow the melting points of each grade. PA6 processes at 240 to 270°C, PA66 at 270 to 300°C, PA12 at 190 to 230°C, and PA1010 at 210 to 250°C. Mold temperatures should be maintained between 60 and 90°C for PA6 and PA66 to ensure proper crystallization, while PA12 and PA1010 mold at 30 to 60°C. Higher mold temperatures improve crystallinity and dimensional stability but extend cycle time by 10 to 20 percent per 10°C increase.

Mold Temperature, Drying, and Cycle Time Optimization

>Injection speed should be moderate to fast for all nylon grades because their relatively low viscosity at processing temperature enables rapid cavity fill. However, excessively fast injection causes jetting and air entrainment in thick sections. Holding pressure of 50 to 80 percent of injection pressure for 2 to 5 seconds is typical, with longer hold times for thicker walls where gate freeze time extends. Screw speed during recovery should be moderate (50 to 100 rpm) to avoid excessive shear heating that can degrade the polymer.

Post-molding annealing is recommended for PA6 and PA66 parts requiring maximum dimensional stability. Annealing at 120 to 150°C for 30 to 60 minutes relieves residual stress and accelerates moisture equilibrium, reducing in-service dimensional change. PA12 and PA1010 generally do not require annealing because their lower moisture absorption limits dimensional shift during service.

What Design Rules Apply to Nylon Injection Molded Parts?

Nylon design follows standard thermoplastic guidelines but requires special attention to moisture-related dimensional change and the high shrinkage rates typical of semi-crystalline materials. Designing for the wet conditioned state rather than the dry-as-molded state is the most common oversight in nylon part design.

Shrinkage rates range from 0.8 to 1.5 percent for unfilled PA6 and PA66, with higher shrinkage in the flow direction than across it due to crystalline orientation. Glass-filled grades reduce shrinkage to 0.3 to 0.8 percent but introduce anisotropic shrinkage that requires careful mold design. PA12 and PA1010 shrink less at 0.5 to 1.0 percent because of their lower crystallinity. Always design tooling to the material supplier’s conditioned-state shrinkage data, not the dry-state values.

Wall Thickness, Ribs, and Draft Angles

>Wall thickness should be uniform and between 1.0 and 3.5mm for optimal cycle time and dimensional control. Nylon’s high shrinkage makes thick sections prone to sink marks and voids. For structural stiffness, use rib reinforcement with rib height up to 3 times wall thickness and rib base width at 50 to 70 percent of wall thickness. Draft angles of 1 to 2 degrees minimum are required for PA6 and PA66 due to their high shrinkage gripping the mold core during cooling.

Metal inserts for threaded assembly are common in nylon parts, particularly PA66 automotive components. The insert boss should have a wall thickness of 1.5 to 2.0 times the insert diameter to prevent cracking during thermal cycling. Preheating metal inserts to 100 to 120°C before molding reduces residual stress at the polymer-metal interface and improves pull-out strength by 20 to 30 percent.

PA6 vs PA66 vs PA12 vs PA1010 — Which Grade for Which Application?

Material selection among the four nylon grades is driven by three practical factors: operating temperature, moisture environment, and cost target. The decision framework below maps each grade to its optimal application space.

What Industries Use Nylon Injection Molded Parts?

Nylon injection molding¹ serves industries where the material’s combination of strength, toughness, chemical resistance, and temperature capability cannot be matched by commodity plastics. Automotive is the largest consumer by volume, followed by electrical and electronics, industrial equipment, and consumer products.

Automotive applications consume over 40 percent of global PA66 production. Under-hood components like intake manifolds, engine covers, and radiator end tanks operate at temperatures above 120°C where PA6 loses stiffness. Electrical connectors, sensor housings, and fuse boxes use flame-retardant PA66 grades (V0 rated) that meet UL94 requirements. Interior trim and structural brackets use PA6 or glass-filled PA6 for cost efficiency where temperature exposure is moderate.

The medical device industry uses PA12 extensively for catheter tubing and fluid handling components where flexibility, biocompatibility, and resistance to sterilization chemicals are required. PA12 grades holding USP Class VI certification enable direct bodily fluid contact, replacing PVC in many applications to eliminate plasticizer leaching concerns that have driven regulatory scrutiny of medical device materials.

Electronics, Medical, and Consumer Applications

>Sporting goods and consumer products leverage PA6 and PA6+GF for skateboarding wheels, ski bindings, helmet buckles, and outdoor equipment hardware. These applications benefit from nylon’s combination of toughness, abrasion resistance, and ability to maintain mechanical properties across temperature ranges from minus 40 to plus 120 degrees Celsius.

Electrical and electronics applications leverage nylon’s excellent dielectric properties and flame retardancy. PA66 grades with red phosphorus or nitrogen-based flame retardants achieve UL94 V0 rating at 0.4mm wall thickness, qualifying them for connectors, switches, and circuit breaker housings. The growing electric vehicle market drives demand for PA66 battery module components that combine flame retardancy with structural performance.

Industrial machinery uses nylon for gears, bearings, bushings, and conveyor components where the material’s low friction coefficient, wear resistance, and ability to run without external lubrication reduce maintenance costs. PA6 and PA66 with PTFE or MOS2 solid lubricant additives are standard for gear applications operating at moderate loads and speeds. For food processing equipment, FDA-compliant PA6 and PA12 grades enable direct food contact without contamination concerns.

Frequently Asked Questions About Nylon Injection Molding

How long should I dry PA6 and PA66 before injection molding?

PA6 and PA66 require 4 to 8 hours of drying at 80 to 100°C in a dehumidifying hopper dryer to reach moisture content below 0.2 percent. The exact time depends on initial moisture level, pellet size, and dryer efficiency. For material that has been stored in high-humidity conditions, extend drying to 8 to 12 hours. Never exceed 12 hours or 110°C as prolonged exposure degrades the polymer and causes yellowing. Monitor moisture content with a Karl Fischer titration test before processing critical parts.

Can PA6 and PA66 be molded on the same machine without modifications?

Yes, PA6 and PA66 can run on the same machine but require different temperature settings and purge procedures. Switching from PA6 to PA66 requires raising barrel temperatures by 20 to 30°C and increasing mold temperature by 10 to 20°C. Always purge thoroughly with the new grade or a compatible purge compound because mixing PA6 and PA66 in the barrel creates grafted copolymer deposits that cause inconsistent processing and surface defects on subsequent production runs.

What happens if nylon is molded without proper drying?

Molding undried nylon causes three progressive problems. First, moisture creates silver streaks (splay) on the part surface as water vapor expands during cavity fill, producing cosmetic rejects. Second, water reacts with amide bonds in the polymer chain through hydrolysis, permanently reducing molecular weight and causing measurable loss in tensile strength and impact resistance. Third, excess moisture lowers melt viscosity unpredictably, causing flash, dimensional variation, and inconsistent fill patterns that make statistical process control impossible.

Is PA12 worth the significant price premium over PA6 for general applications?

For general-purpose applications where moisture absorption is tolerable and operating temperatures stay below 120°C, PA6 is the correct economic choice and PA12 offers no functional advantage to justify its 3 to 5 times higher cost. PA12 becomes worthwhile only when the application demands dimensional stability in humid or wet environments, chemical resistance to fuels and hydraulic fluids, or flexibility at low temperatures where PA6 becomes brittle. Fuel lines, pneumatic tubing, and medical catheter components are typical applications that justify PA12 pricing.

How does glass fiber reinforcement affect nylon injection molding processing?

Glass-filled nylon grades (typically 30 percent short glass fiber) require 10 to 20°C higher melt temperatures and 10 to 15 percent higher injection pressures than unfilled grades because the fibers increase melt viscosity. Screw wear accelerates significantly — expect 2 to 3 times faster wear on screw flights and barrel lining compared to unfilled nylon processing. Mold surfaces also wear faster, particularly at gate locations where fiber-laden melt impinges at high velocity. Budget for more frequent mold maintenance and screw inspection when running glass-filled nylon in volume.

What is the difference between conditioned and dry-as-molded nylon properties?

Dry-as-molded properties are measured immediately after molding when moisture content is below 0.2 percent, representing the material in its stiffest and strongest state. Conditioned properties are measured after the part reaches moisture equilibrium at 23°C and 50 percent relative humidity, typically 2.5 to 3.0 percent moisture for PA6 and PA66. Conditioning reduces tensile strength by 30 to 40 percent and stiffness by 50 to 60 percent, but dramatically improves toughness and impact resistance. Always design to conditioned properties for applications exposed to ambient humidity.

Why ZetarMold for Nylon Injection Molding?

🏭 ZetarMold Factory Insight
Our Shanghai facility processes PA6, PA66, PA12, and glass-filled nylon grades daily across 45 machines from 90T to 1850T. In 2025, we produced over 300,000 nylon components for automotive and industrial clients, including PA66 intake manifold brackets and PA12 fuel line fittings requiring dimensional tolerances of plus or minus 0.05mm. Our 8 engineers each bring 10+ years of nylon processing experience with in-house moisture analysis capabilities.

Nylon molding demands precise moisture control and temperature management that our engineering team delivers consistently. We maintain dedicated hopper dryers for each nylon grade to prevent cross-contamination and run automated moisture monitoring before every production shift. For complex injection mold design² challenges in glass-filled nylon, our engineering team provides DFM feedback within 48 hours.

Ready to start your nylon molding project? injection molding service³ for material selection guidance across PA6, PA66, PA12, and PA1010 grades, with comprehensive tooling quotations delivered within 5 business days.

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1. nylon injection molding: This refers to the manufacturing process of shaping polyamide thermoplastic materials using injection molding equipment to produce engineering components with high strength and chemical resistance. ↩

2. injection mold design: This refers to the engineering discipline encompassing tool geometry, cooling channel layout, gate placement, and ejection system optimization for producing dimensionally accurate plastic parts. ↩

3. injection moulding: This is a polymer shaping process in which heated thermoplastic material is forced into a closed mould under pressure, where it cools and solidifies into the final part geometry. ↩