For general-purpose fabrication, PA 6 and PA 6/6 remain the default polyamides, with PA 12 and PA 11 filling the moisture-sensitive, chemical-resistant, and flexible-fillet niches where PA 6/6 absorbs too much water or cracks on impact [S1][S4].
Selection is driven by four measurable properties: moisture absorption (roughly 2.5-3% by weight for unfilled PA 6/6 in humid service), melting point (about 255 degrees C for PA 6/6 vs 220 degrees C for PA 6), impact performance, and chemical resistance. PA 6/6 is the structural workhorse, PA 12 sits at roughly one-fifth the moisture absorption of PA 6/6, and PA 11 gives the toughest, lowest-water-pickup long-chain option for outdoor or fluid-contact parts [S4][S5].
Nylon grade family at a glance: chemistry, melting point, moisture
PA 6 is polymerized from caprolactam, has a melting point near 220 degrees C, and is somewhat more flexible than PA 6/6, which improves impact resistance in thin sections [S4]. PA 6/6 (polyhexamethylene adipamide) melts near 255 degrees C and is stiffer and stronger at room temperature, making it the first-choice grade for structural brackets, gears, fasteners, and load-bearing clips in automotive and industrial assemblies [S4].
PA 12 is a long-chain polyamide with the lowest moisture absorption of the common grades, roughly one-fifth that of PA 6/6, and is also the most tested polyamide for powder-bed additive manufacturing [S4][S6]. PA 11 is a bio-based long-chain polyamide with strong dimensional stability, low moisture pickup, and good chemical and environmental stress-cracking resistance, and it is the most flexible of the four grades [S4][S5].
Mechanical and thermal spec map: which grade does what
Across the four grades, the spec trade-off lines up as follows. PA 6/6 leads on stiffness, tensile strength at room temperature, and heat resistance, but absorbs 2.5-3% moisture by weight in humid service, which causes measurable swelling and stiffness loss [S4]. PA 6 trades a 35 degrees C lower melting point and slightly higher moisture pickup for better thin-section impact, which is why it shows up in automotive housings, electrical connectors, and consumer-goods enclosures [S4].
PA 12 trades ultimate stiffness and heat resistance for the lowest water absorption, a roughly 178 degrees C melting point, and good abrasion and fatigue behaviour, which is why it is widely used for fluid-contact tubing, cable jacketing, and selective-laser-sintered parts [S4][S7]. PA 11 trades higher cost for the best balance of flexibility, low-temperature toughness, and chemical resistance in the family, and is commonly specified where the part must flex repeatedly or sit in outdoor or hydrocarbon exposure [S4][S5]. For comparison with higher-end thermoplastics used in similar load-bearing roles, the PAEK family spec map covers the temperature and chemical tier above PA 6/6. For general fabrication material selection that sits alongside nylon, the industrial rubber spec map covers elastomer equivalents for sealing and flex roles. For the broader engineering-plastic landscape, the five-major-grades engineering-plastic map places PA 6/6 against POM, PC, PET, and ABS.
Selection criteria: moisture, tolerance, temperature, chemistry
The first decision is moisture exposure. If the part runs in a controlled indoor environment and tight tolerances are not critical, PA 6/6 is the cost-effective default; if the part sees outdoor humidity, wet fuel, or glycol, the dimensional swing of unfilled PA 6/6 will push the design toward PA 11 or PA 12 [S4]. Nylon is a hygroscopic semi-crystalline thermoplastic, and moisture sensitivity varies substantially by grade, which is why no single grade is the best fit for every molded part [S4].
The second decision is operating temperature. PA 6/6 at 255 degrees C melting point tolerates higher continuous service temperatures than PA 6 (220 degrees C) and PA 12 (about 178 degrees C), so under-hood, electrical-connector, and powertrain parts default to PA 6/6, while low-temperature flexible parts default to PA 11 [S4][S5]. The third decision is chemical and stress-cracking exposure: PA 11 and PA 12 resist hydrocarbons, zinc chloride, and many solvents better than PA 6/6, and PA 12 is also widely used for its abrasion and fatigue behaviour in 3D-printed functional parts [S4][S7].
Process-specific guidance: injection molding, extrusion, and 3D printing
For injection molding, PA 6 and PA 6/6 dominate because they flow well, fill thin sections, and deliver the best stiffness-to-cost ratio for high-volume automotive and industrial parts [S1][S4]. Drying is non-negotiable: PA 6/6 stored at room humidity must be dried before molding to avoid hydrolysis, steam streaks, and brittle parts, which is the single most common cause of field failures in unfilled PA 6/6 moldings [S4].
For 3D printing, the Prusa knowledge base notes that nylon is often selected for printed gears and bushings because of its low friction and toughness, and the Bambu Lab community discussion recommends PA 12 or PA 11 filaments for thin, slightly flexible parts where PA 6 and PA 6/6 are too stiff and ABS/ASA are too brittle [S3][S5]. Powder-bed fusion of PA 12 is the most established additive route, and PA 12 is also a strong selection for applications where abrasion and fatigue are dominant, with good chemical resistance [S6][S7].
Comparison: PA 6 vs PA 6/6 vs PA 11 vs PA 12
On melting point, PA 6/6 (~255 degrees C) > PA 6 (~220 degrees C) > PA 11 (~190 degrees C) > PA 12 (~178 degrees C) [S4]. On stiffness at room temperature, PA 6/6 > PA 6 > PA 12 > PA 11, and on flexibility and impact, the order reverses [S4][S5]. On moisture absorption, PA 12 is the lowest at roughly one-fifth of PA 6/6, PA 11 is the next lowest, and PA 6/6 is the highest at 2.5-3% by weight in humid service [S4].
On chemical resistance, PA 11 and PA 12 lead for hydrocarbons, fuels, and environmental stress-cracking, while PA 6/6 leads for heat and structural load [S4][S7]. On cost and availability, PA 6 and PA 6/6 are the cheapest and most widely stocked grades and are used in many applications due to their excellent performance/cost ratios; PA 11 and PA 12 sit at a premium and are chosen only when PA 6/6 cannot meet the moisture or chemistry spec [S1][S4].
Limitations and failure modes to design around
Every nylon grade fails in the same family of ways: moisture-driven dimensional change, hydrolysis at high temperature in the presence of water, UV-driven embrittlement in outdoor service without stabilization, and notch-sensitive brittle fracture in cold conditions for PA 6/6 [S4]. The cure is grade selection, not additive rescue: specifying PA 12 for an outdoor fluid-handling part, or PA 11 for a flexing clip, removes the failure mode at the material-decision step rather than chasing it with a black-box additive package [S4][S5].
PA 6/6 also loses stiffness as it picks up moisture, which is why unfilled PA 6/6 in a humid environment can absorb 2.5-3% moisture by weight and show measurable dimensional change and stiffness loss; the same property that makes PA 6/6 tough when dry makes it the wrong choice for a tight-tolerance wet part [S4].
Standards and sourcing
Nylon resin is commonly specified against ISO and ASTM material designations (for example ISO 1874 for polyamide molding and extrusion compounds, and ASTM D6779 for PA 6 and PA 66), and additives such as glass fibre, carbon fibre, and impact modifiers are called out on the resin data sheet [S1]. For moisture-content control on the shop floor, the resin supplier's drying recommendations (typically 80-100 degrees C for 4-8 hours for PA 6/6) are the practical baseline and are the difference between a good molding and a brittle field failure [S4].
For supply chain, PA 6 and PA 6/6 are global commodity polyamides; PA 12 and PA 11 are sourced from a smaller set of long-chain polyamide producers and carry longer lead times, which is a procurement constraint independent of the engineering spec [S1][S4].
For related polymer-side selection, the engineering-plastic map for electronics extends nylon selection into insulating and flame-retardant grades, and the industrial solvent types and selection criteria reference covers the chemical side of compatibility when a nylon part must survive solvent exposure. Trackable signals: any shift in long-chain PA 11/PA 12 capacity announcements, and any new datasheet revisions from major polyamide producers on moisture-conditioned (vs dry-as-molded) mechanical values.
Spec-level background on the components involved: nylon, pressure transmitter, and flow meter.