PA6 vs PA66 vs PA12: Nylon Grades Compared — Properties, Modifications, and When to Switch Materials

PA6, PA66, and PA12 are the three most common CNC-machinable nylon grades. At 23°C dry-as-molded (DAM) per ISO 527, PA6 yields 75–83 MPa tensile strength, PA66 yields 83 MPa (Zytel 101L), and PA12 yields 61 MPa (Zytel 158L). Heat deflection temperature at 1.82 MPa per ASTM D648: PA6 65–80°C, PA66 90°C, PA12 65°C. Twenty-four-hour water absorption per ASTM D570: PA6 approximately 1.2%, PA66 1.20% (Zytel 101L), PA12 0.25% (Zytel 158L).

Moisture is where the grades split in ways that matter on a finished part. PA66 (Zytel 101L) tensile yield stress: 83 MPa at 23°C DAM, 53 MPa at 50% RH equilibrium (ISO 527). That 36% drop happens in storage, not in a test lab. A PA66 bore machined to 30.000 mm can measure 30.180 mm after reaching moisture equilibrium at 100% RH (0.6% linear growth at 50% RH, 2.6% at saturation, per DuPont Module II Nylon). PA12 saturates at 3.0% water absorption versus PA66’s 8.5% (ASTM D570, Zytel 158L vs 101L). That gap drives PA12’s 2–3x cost premium and its use in precision wet-environment assemblies.

This guide covers unfilled PA6, PA66, and PA12 for CNC machining, plus GF30-reinforced grades, MoS2 and PTFE tribological modifications, and six data-backed conditions for switching grades. Thermal data is from ASTM D648-01 and ASTM D3418. Chemical resistance data is from Zytel/Minlon Design Module 2 immersion testing. All tensile values are ISO 527 or ASTM D638 as noted per source.

1. Why These Three Grades Differ: The Amide Density Rule

Every performance gap between PA6, PA66, and PA12 traces to one structural variable: how many carbon atoms sit between each amide group (-CONH-) along the polymer chain. PA6 puts one amide group every 6 carbons. PA12 puts one every 12. That spacing controls how much water the material absorbs, how stiff it stays when wet, how low a temperature it can take before embrittlement, and how aggressively acid attacks it.

Engineering note: When your part needs to hold ±0.02 mm in a humid factory, the amide density is the number to look at, not the room-temperature tensile strength. PA66 and PA6 are nearly identical at 23°C DAM on strength. They diverge sharply once humidity or temperature enters the picture. For the full six-property selection framework covering all nylon grades, see the nylon polyamide properties selection guide.

Table 1. Molecular structure and key physical constants, PA6 / PA66 / PA12

	PA6	PA66	PA12
Synthesis route	Ring-opening, caprolactam	Condensation, hexamethylenediamine + adipic acid	Ring-opening, laurolactam
Carbons per amide group	6	6 (alternating 6+6)	12
Crystal structure	Less symmetric	More symmetric, tighter packing	Looser, longer spacing
Melting point (ASTM D3418)	220°C	262°C	175–180°C
Density (ISO 1183)	1.12–1.15 g/cm³	1.13–1.15 g/cm³	1.01–1.02 g/cm³
Saturation water absorption (ASTM D570)	7–9%	8.5% (Zytel 101L)	3.0% (Zytel 158L)
Low-temp embrittlement (ASTM D746)	approx. -80°C	-80°C (Zytel 101L DAM)	-126°C (Zytel 158L DAM)
Tensile modulus 23°C DAM (ISO 527)	approx. 2500 MPa	3100 MPa (Zytel 101L)	2034 MPa (Zytel 158L)

Sources: ASTM D3418, D746, D570, ISO 527; Zytel 101L and 158L from DuPont Module II Nylon; PA6 from CAMPUS database. Comparable data applies to BASF Ultramid B (PA6) and Ultramid A (PA66) grades tested under ISO 527 and ISO 75.

2. Side-by-Side Property Data

PA66 dry-as-molded at 23°C delivers 83 MPa tensile strength (ASTM D638, Zytel 101L DAM). At 50% RH equilibrium that number drops to 77 MPa, a 7% loss. Flexural modulus falls from 2827 MPa to 1207 MPa, a 57% drop (ASTM D790, 23°C). PA12 (Zytel 158L) loses proportionally less: flexural modulus 2034 MPa DAM to 1241 MPa at 50% RH, a 39% drop. The grade that looks weaker on a dry datasheet often holds its shape better once the part sits in a real environment.

Engineering note (Dewey Wu): “When we quote a nylon CNC part, the first question is where the part lives after delivery. A PA66 bracket machined to print at 23°C DAM has 36% less yield stress once it equilibrates to 50% RH — 83 MPa becomes 53 MPa (ISO 527, Zytel 101L). If the design safety factor was tight to begin with, it fails in the field, not in incoming inspection.”

Table 2. Core property comparison across five nylon grades (23°C DAM unless noted)

Property	PA6 unfilled	PA66 unfilled (Zytel 101L)	PA66 50%RH (Zytel 101L)	PA12 unfilled (Zytel 158L)	PA66 GF33 (Zytel 70G33L)
Tensile strength, 23°C DAM	70–85 MPa	83 MPa	77 MPa	61 MPa	186 MPa
Tensile strength, 77°C DAM	—	62 MPa	41 MPa	41 MPa	110 MPa
Flexural modulus, 23°C	2000–3000 MPa	2827 MPa	1207 MPa	2034 MPa	8963 MPa
Notched Izod 23°C DAM	4–8 kJ/m²	53 J/m	112 J/m	53 J/m	117 J/m
HDT at 1.82 MPa, DAM	65–80°C	90°C	—	65°C	249°C
Melting point	218–222°C	262°C	—	175–180°C	262°C
24h water absorption	1.0–1.5%	1.20%	—	0.25%	0.7%
Saturation water absorption	7–9%	8.5%	—	3.0%	5.4%
CoF vs steel, dry	0.25–0.35	0.17–0.43	—	0.25–0.35	0.30–0.40
Relative material cost	1.0x	1.1–1.3x	—	2.0–3.0x	1.8–2.2x

Sources: Zytel 101L and 158L from DuPont Module II Nylon (ASTM D638, D790, D648, D570, D3418, D256); PA6 from CAMPUS database; PA66 GF33 from Zytel 70G33L (DuPont Module II).

2.1 Three things a datasheet number will not tell you

Table 2A. Three datasheet reading traps with actual numbers

Trap	Datasheet says	Reality	Specific data
DAM tensile is not a service value	PA66: 83 MPa at 23°C DAM	77 MPa at 23°C 50%RH; 62 MPa at 77°C DAM; 41 MPa at 77°C 50%RH	ASTM D638, Zytel 101L, DuPont Module II
% water absorption ≠ % dimensional change	PA66: 8.5% saturation absorption	50%RH = +0.6% linear growth; 100%RH = +2.6%. Ratio: approx 0.2–0.3% dim change per 1% moisture gain	Minlon/Zytel Design Module 2; DuPont Module II
Isotropic assumption on CNC rod is wrong	Datasheet gives one value	PA6 (Zytel 7300): flow direction +0.22%, transverse +0.40% at 50%RH. Round bore becomes slightly oval.	ISO 1110, 2 mm specimen, 64 days, Minlon/Zytel Design Module 2

Engineering note: A CAE model run on 23°C DAM values produces an optimistic prediction for any nylon part that will live in a warm or humid environment. Run the model at the 50%RH conditioned values for structural parts in ambient air; run it at 77°C DAM values for underhood or elevated-temperature service. The gap between the two sets of inputs is the hidden safety factor your design either has or does not.

EPOC CRAFTER machines all three grades in stock rod and plate form; see the nylon and engineering plastics material options for available specifications.

3. How Modifications Change the Numbers

GF30 reinforcement turns PA66 from a general-purpose structural polymer into a metal-replacement candidate. Zytel 70G33L at 23°C DAM: tensile strength 186 MPa, flexural modulus 8963 MPa, HDT at 1.82 MPa 249°C (ASTM D638, D790, D648). Unfilled Zytel 101L at the same conditions: 83 MPa, 2827 MPa, 90°C. The glass fiber does not change the PA66 base chemistry; it transfers load away from the polymer matrix and into the fibers.

One boundary condition that catches engineers: DuPont General Design Principles (page 73) explicitly states that glass-reinforced Zytel should be avoided for gears and considered only for short-time, intermittent operation with full testing. Hard GF particles abrade the mating tooth surface. For gear applications, unfilled PA66 or MoS2-modified grades are the correct starting point.

Table 3. GF reinforcement impact: PA66 unfilled vs GF33 (Zytel 101L vs 70G33L)

Property	PA66 unfilled (Zytel 101L)	PA66 GF33 (Zytel 70G33L)	Change
Tensile strength 23°C DAM (ASTM D638)	83 MPa	186 MPa	+124%
Tensile strength 23°C 50%RH	77 MPa	124 MPa	+61%
Flexural modulus 23°C DAM (ASTM D790)	2827 MPa	8963 MPa	+217%
Flexural modulus 23°C 50%RH	1207 MPa	6205 MPa	+414%
HDT at 1.82 MPa DAM (ASTM D648)	90°C	249°C	+177%
24h water absorption (ASTM D570)	1.20%	0.7%	-42%
Notched Izod 23°C DAM (ASTM D256)	53 J/m	117 J/m	+121%
CLTE, flow direction	81×10⁻⁶ /°C	23×10⁻⁶ /°C	-72%
Weld line strength retention	baseline	approx. 60% of unfilled	-40% at welds

Sources: DuPont Module II Nylon (Zytel 101L, 70G33L); Minlon/Zytel Design Module 2; DuPont General Design Principles.

3.1 MoS2 and PTFE grades for sliding contact

Unfilled PA66 (Zytel 101F) against steel at 0.14 MPa contact pressure and 0.5 m/s surface speed: kinetic CoF range 0.17–0.43. Against Delrin (POM): kinetic CoF 0.08–0.11. Against another Zytel surface: 0.11–0.19. Maximum PV for Zytel 101 running on hardened steel without lubrication: 0.1 MPa·m/s (Minlon/Zytel Design Module 2).

Engineering note: Gear pairing matters more than grade alone. Zytel 101 running against Delrin (POM) drops dynamic CoF to 0.08–0.11 under the same conditions where Zytel against Zytel runs 0.11–0.19. Specifying a PA66/POM gear pair gives you better friction numbers than switching to an MoS2 grade and keeping both gears in nylon.

Table 4. Modification summary for PA66 grades

Modification	Grade example	Primary gain	Primary tradeoff	Suitable for gears
None	Zytel 101L	Balanced properties, toughness	Lower stiffness and HDT versus GF	Yes, preferred
GF33	Zytel 70G33L	2.2x strength, 249°C HDT	Weld line -40%, thread cut only, no gears	No (short-time only)
MoS2	Various PA66	Lower CoF for dry sliding	Small strength reduction (~5–10%)	Yes, preferred for dry run
PTFE-filled	Various PA66	Lowest CoF for wear pads, bushings	Reduced strength	Yes, bushing applications
Kevlar 20%	SFC 70K20	5x wear resistance vs unfilled	Higher cost, anisotropic	No data; specialized
Supertough	Zytel ST801	Notched Izod >910 J/m (ASTM D256, 23°C DAM)	Lower stiffness, lower HDT	No

Sources: DuPont Module II Nylon; Minlon/Zytel Design Module 2; DuPont General Design Principles.

For prototypes where GF30 CNC stock is not yet procured, PA12 powder in SLS is an alternative path; see EPOC CRAFTER’s additive manufacturing and 3D printing capabilities for lead time comparison.

4. Thermal Performance: Where the 40°C Gap Becomes Decisive

PA66 and PA6 differ by roughly 8–10 MPa in dry tensile strength at 23°C. The HDT numbers are where they stop being interchangeable. PA66 (Zytel 101L) at 1.82 MPa: 90°C. PA6 typical range at the same load: 65–80°C. PA12 (Zytel 158L): 65°C. Those are ASTM D648 DAM values.

Engineering note: The correct question is not what is the HDT. It is what is the service temperature, what is the sustained load, and how long does the part need to hold dimension. Continuous-use temperature limits, if stated, are separate values from UL or equivalent certification and typically run well below HDT.

Table 5. Tensile strength vs temperature, three grades (ASTM D638, DuPont Module II Nylon)

Temperature and condition	PA66 unfilled (Zytel 101L)	PA12 unfilled (Zytel 158L)	PA66 GF33 (Zytel 70G33L)
-40°C DAM	114 MPa	94 MPa	214 MPa
23°C DAM	83 MPa	61 MPa	186 MPa
23°C 50%RH	77 MPa	51 MPa	124 MPa
77°C DAM	62 MPa	41 MPa	110 MPa
77°C 50%RH	41 MPa	37 MPa	86 MPa
121°C DAM	43 MPa	—	—
121°C 50%RH	38 MPa	30 MPa	—
HDT at 1.82 MPa DAM (ASTM D648)	90°C	65°C	249°C

5. Moisture and Dimensional Stability: The PA12 Case

PA12 (Zytel 158L) 24-hour water absorption: 0.25% (ASTM D570, 23°C). PA66 (Zytel 101L): 1.20%. Saturation: PA12 3.0%, PA66 8.5%. The 4.8x gap in 24-hour absorption and the 2.8x gap at saturation both trace to amide group density, as covered in Section 1. A part machined to tolerance at 23°C DAM will move as it absorbs moisture in service.

Table 6. Dimensional change, nylon 66 and PA6 at moisture equilibrium

Condition	Material	Linear dimensional change	Engineering implication
50%RH equilibrium	Nylon 66	+0.6%	30 mm bore grows 0.18 mm — exceeds ±0.05 mm tolerance
100%RH / water immersion	Nylon 66	approx. +2.6%	50 mm bore grows 1.3 mm — critical for any fit
50%RH, flow direction (ISO 1110)	PA6 (Zytel 7300)	+0.22%	Anisotropic: round bore becomes oval
50%RH, transverse (ISO 1110)	PA6 (Zytel 7300)	+0.40%	Transverse growth 1.8x flow direction
100%RH, flow direction (ISO 1110)	PA6 (Zytel 7300)	+1.20%	Full saturation: significant bore shift
100%RH, transverse (ISO 1110)	PA6 (Zytel 7300)	+2.00%	5x the 50%RH transverse value

Source: Minlon/Zytel Design Module 2. PA12 (Zytel 158L) saturation absorption is 3.0% vs PA66’s 8.5% (ASTM D570). Direct ISO 1110 dimensional data for Zytel 158L not extracted; dimensional change scales with moisture uptake and will be substantially lower than PA66 figures.

EPOC CRAFTER machines PA12 rod and plate stock at both Asheboro, NC and Shenzhen facilities; tolerances achievable on PA12 CNC parts are covered on the CNC machining capabilities page.

6. Chemical Resistance by Grade

PA66 (Zytel 101) resists all aliphatic and aromatic hydrocarbons, most salts, glycols, and ketones at 23°C. Three categories attack it: phenols (direct solvent), mineral acids above 5% concentration, and oxidizing agents. GF content does not change these chemical boundaries — it changes stiffness and HDT only. PA12 extends resistance in mild organic acid service by approximately 3x the duration before failure (Minlon/Zytel Design Module 2).

Engineering note: Chemical resistance data in the table below is from immersion testing of unstressed specimens. Stressed parts in the same chemical fail sooner. DuPont General Design Principles notes explicitly that some materials unaffected by a reagent in the unstressed state will stress crack under combined mechanical and chemical exposure. Verify chemical compatibility with the actual stress state, temperature, and exposure duration of the application. PA12’s advantage in chemical environments, like its moisture performance, traces directly to its lower amide density and the reduced number of polar bonding sites per unit chain length.

Table 7. Chemical resistance by rating, PA66 (Zytel 101) and PA12 (Zytel 158), 23°C baseline

Chemical	Conc.	PA66 Rating	PA66 Exposure / Note	PA12 Rating	PA12 Exposure / Note
Acetone	100%	Excellent	365 d (23°C and 50°C)	Excellent	90 d, dim +0.2%
Toluene	100%	Excellent	365 d at 50°C	—	—
Xylene	100%	Excellent	—	—	—
Ethylene glycol	100%	Excellent	56 d	—	—
Ethanol	95%	—	—	Excellent	90 d, wt +3.2%, dim minimal
Lactic acid	10%	Excellent	316 d at 35°C	—	—
Citric acid	10%	Satisfactory	77 d at 35°C	—	—
Acetic acid	5%	Satisfactory→Unsat.	Satisfactory 30 d; Unsat. at 70 d	Satisfactory	90 d, dim +0.5%
NaOH	10%	Excellent→Unsat.	Excellent 30 d at 70°C; Unsat. 365 d	—	—
Sodium chloride	10%	Excellent	365 d	—	—
Carbon tetrachloride	100%	—	—	Excellent	365 d, dim 0%
n-Butanol	100%	—	—	Satisfactory	90 d, dim +0.3%
Hydrochloric acid	2.5%	Excellent	10 d only	—	—
Hydrochloric acid	10%	Unsatisfactory	60 d	—	—
Sulphuric acid	30%	Unsatisfactory	30 d	—	—
Sulphuric acid (conc.)	conc.	Serious attack	1500 h on GF30 PA66	—	—
Nitric acid	10%	Unsatisfactory	60 d	—	—
Formic acid	90%	Unsatisfactory	Solvent for nylon 66	—	—
Phenol	90%	Unsatisfactory	Solvent for nylon	Serious attack	GF30, 1500 h
Calcium chloride	5%	Unsatisfactory	Stress cracking at 60°C	—	—
Petrol/gasoline	100%	Excellent	GF30: no stress crack at 93 MPa, 5 min	—	—
Lubricating oil	100%	Excellent	GF30: no stress crack at 93 MPa, 5 min	—	—

Source: Minlon/Zytel Design Module 2, pages 45–48. All values unstressed immersion specimens at 23°C unless noted. Stressed parts fail sooner. Every 15°C above 23°C reduces chemical service life by 25–50% (page 44). Zinc chloride causes stress cracking in loaded PA66.

7. CNC Machinability Notes

Unfilled PA6 and PA66 rod and plate machine with HSS tooling. GF30 grades require carbide. That distinction is not a preference; glass fibers at 30 wt% content abrade HSS at a rate that makes the tooling economically nonviable within a short run. Ensinger’s machining guide states directly: non-reinforced thermoplastics can be machined with HSS; reinforced materials require hard metal tools.

7.1 Tooling by grade

Table 8A. Thread operation selection by tensile modulus (DuPont General Design Principles, page 75)

Tensile modulus	Thread method	Grade examples	Notes
Below 1500 MPa	Thread forming viable	Flexible nylon grades, PA12 50%RH (1241 MPa)	Self-tapping screws acceptable
1500–3000 MPa	Forming possible; cutting preferred	PA6 unfilled (~2500 MPa), PA12 DAM (2034 MPa)	Zytel grades: cutting preferred
Above 3000 MPa	Thread cutting only	PA66 unfilled (3100 MPa), PA66 GF13	PA66 sits above threshold; cut all threads
Above 7000 MPa	Thread cutting only; brittle response risk	PA66 GF30 (~9000 MPa), PA66 GF43	Reduce feed, monitor for cracking

Source: DuPont General Design Principles, page 75. Modulus values from ISO 527/ASTM D790, 23°C DAM.

Table 8. CNC machinability summary by grade

Grade	Tooling	Thread method	Cooling	Pre-condition if cracking	Post-machining movement at 50%RH
PA6 unfilled	HSS or carbide	Cut preferred (mod ~2500 MPa)	Pure water or dry	Condition to ~2% moisture	+0.22% flow / +0.40% transverse
PA66 unfilled	HSS or carbide	Cut only (mod 3100 MPa)	Pure water or dry	Condition to ~2% moisture	+0.6% linear
PA66 GF30/33	Carbide required	Cut only (mod ~9000 MPa)	Pure water or dry	Less risk, lower moisture uptake	Lower than unfilled; verify by grade
PA12 unfilled	HSS or carbide	Cut preferred	Pure water or dry	Rarely needed	Significantly lower than PA66

Sources: Ensinger Machining Guide; DuPont General Design Principles pages 75, 149, 151; Minlon/Zytel Design Module 2 pages 55–56; ASTM D570.

For tight-tolerance nylon CNC parts with post-delivery humidity specifications, EPOC CRAFTER’s DFM review process covers material state, conditioning, and tolerance allowance before quoting.

8. When to Switch: 6 Specific Trigger Conditions

Grade switching decisions that rest on “it depends on the application” are not decisions. Each of the six triggers below has a data-backed threshold, a switch direction, and at least one condition that does not activate the switch. Triggers 1, 2, and 3 temperature, tensile strength floor, and post-delivery tolerance, cover more than 80% of real grade change decisions.

Table 9. Six switching trigger conditions

Trigger	Threshold	Switch direction	Does not trigger when
Continuous service temperature	Above 100°C	PA6 to PA66; above 150°C loaded, PA66 unfilled to GF30 (HDT 249°C)	Below 80°C dry indoor service
Tensile strength floor	Above 120 MPa	Any unfilled to PA66 GF30/33 (186 MPa DAM)	Gear applications: use unfilled PA66
Post-delivery tolerance in humidity	Below ±0.05 mm with humidity variation	PA6 or PA66 to PA12	Controlled humidity environment or tolerance above ±0.10 mm
Mild organic acid contact duration	Acetic acid 5% beyond 30 days at 23°C	PA66 to PA12	Short-duration splash or alkaline environments
Impact loading temperature	Below -60°C	PA66 to PA12 (embrittlement -126°C DAM vs -80°C DAM, ASTM D746)	Static loads only
Leave polyamide family	Dry precision dims, or T above 150°C sustained, or strong acid + high temperature	PA66 to POM for friction pairs; nylon to PEEK for T above 150°C	Below 150°C continuous temperature: PA66 GF30 covers most structural needs

Sources: DuPont Module II Nylon; Minlon/Zytel Design Module 2; DuPont General Design Principles; ASTM D746, D648, D570.

For automotive underhood or electronics enclosure applications where grade selection feeds directly into procurement, see EPOC CRAFTER’s industry-specific CNC manufacturing capabilities.

9. Nylon vs POM vs PEEK: When to Leave the Polyamide Family

PA66 and POM (acetal) are not interchangeable substitutes. Each outperforms the other on specific, testable criteria. Three decision points below determine which material’s binding constraint matches your application requirement.

Table 10. Nylon vs POM vs PEEK decision matrix

Criterion	PA66 unfilled	PA66 GF30	POM (Delrin)	PEEK
Post-delivery dimensional stability (humid)	Poor: +0.6% at 50%RH	Better: lower moisture uptake	Excellent: under 0.2%	Excellent
Tensile strength 23°C DAM	83 MPa	186 MPa	~70 MPa	~100 MPa unfilled
Continuous load temp (practical ceiling)	80–100°C	approx 150°C	approx 90°C	250°C
Repeated impact (2.16 m/s)	250 impacts to failure	Lower than unfilled	185 impacts	Lower than PA66 unfilled
Dynamic CoF vs mating PA66 (dry, 0.14 MPa)	0.11–0.19 (PA66/PA66)	0.30–0.40	0.08–0.11 as mating material	Varies
Strong acid resistance	Attacked at 10% HCl, 30% H2SO4	Same as base polymer	Better in dilute acid	Excellent
Relative material cost	1.1–1.3x vs PA6	1.8–2.2x vs unfilled PA66	1.0–1.2x vs PA6	10–20x vs PA66

Sources: DuPont General Design Principles pages 54, 69; Minlon/Zytel Design Module 2 pages 25, 29; ASTM D648, D570; CAMPUS database typical values for POM and PEEK.

10. Quick Selection Summary

Five questions narrow the nylon grade selection before you open a datasheet. Running all five takes under two minutes and eliminates at least two grades in most applications.

Table 11. Nylon grade quick selection matrix

Question	Condition	Recommended grade	Exclude / Note
1. Continuous service temperature under load	Above 150°C	PA66 GF30/33 (HDT 249°C at 1.82 MPa)	PA6, PA66 unfilled, PA12
	100–150°C	PA66 GF30/33	PA6, PA12
	80–100°C	PA66 unfilled (HDT 90°C)	PA6 (HDT 65–80°C), PA12 (HDT 65°C)
	Below 80°C	PA6 or PA12 (go to Q2–Q5)	—
2. Minimum tensile strength at 23°C DAM	Above 120 MPa	PA66 GF30/33 (186 MPa)	All unfilled grades
	75–120 MPa	PA66 unfilled (83 MPa)	PA12 (61 MPa)
	Below 75 MPa / flexibility required	PA6 or PA12	PA66 GF30/33
	Gear application	PA66 unfilled or PA66 MoS2	PA66 GF30/33 — abrades mating surface (DuPont GDP p.73)
3. Post-delivery tolerance and humidity	Below ±0.05 mm, variable humidity	PA12 (saturation 3.0% vs PA66 8.5%)	PA6, PA66 — PA66 grows +0.6% at 50%RH; 30 mm bore = 0.18 mm shift
	±0.05–0.10 mm, variable humidity	PA66 may hold; verify per ISO 1110	PA6 — higher anisotropic movement
	Above ±0.10 mm, any humidity	PA6 or PA66 acceptable	—
4. Chemical exposure	Mild organic acid (acetic acid 5%) beyond 30 d	PA12 (Satisfactory 90 d vs PA66 Unsat. at 70 d)	PA66
	Strong acid (HCl 10%, H2SO4 30%), phenol	No polyamide — evaluate PEEK or thermoset	All PA grades
	Fuels, lubricants, glycols, ketones, aromatics	PA66 or PA6 (Excellent at 23°C)	—
	Zinc/calcium chloride above 50°C under load	PA612 (Zytel 151) or PA12	PA66 — stress cracking risk
5. Sliding contact or gear	Gear, continuous contact loading	PA66 unfilled (fatigue 25 MPa at 10⁶ cycles init. lub.; 40 MPa continuous)	PA66 GF30/33
	Gear mating pair, friction minimization	One PA66 + one POM (CoF 0.08–0.11 vs PA66/PA66 at 0.11–0.19)	Both gears same material
	Dry sliding bushing	PA66 MoS2 or PTFE-filled PA66	—
	Oil-lubricated sliding	PA66 unfilled (CoF 0.02–0.11 at 0.75 m/s with oil)	—

Sources: DuPont Module II Nylon; Minlon/Zytel Design Module 2; DuPont General Design Principles; ASTM D638, D648, D570, D746.

EPOC CRAFTER machines PA6, PA66, PA66 GF30, and PA12 at CNC facilities in Asheboro, NC and Shenzhen. Free DFM review covers material state specification, post-delivery conditioning requirements, and tolerance stack against moisture movement. Download the Nylon Grade Selection Checklist to run these questions against your part before requesting a quote, or

submit your drawing directly for a 12-hour quote.

11. FAQ

What is the difference between PA6 and PA66?

PA6 and PA66 are both polyamide grades with identical amide group density (one amide group per 6 carbon atoms), but different molecular architecture. PA66 is synthesized from two alternating monomers producing a tighter, more symmetric crystal structure. That difference gives PA66 a melting point of 262°C versus PA6’s 220°C (ASTM D3418), dry tensile modulus of 3100 MPa versus approximately 2500 MPa for PA6 (ISO 527, 23°C DAM), and HDT at 1.82 MPa of 90°C versus PA6’s 65–80°C (ASTM D648). In CNC machining, PA6 is the lower-cost starting point for parts operating below 80°C without high stiffness requirements. PA66 is specified when service temperature exceeds 80°C or when the additional 10 MPa dry tensile strength is needed for load-bearing geometries.

Why does PA12 absorb less water than PA6?

PA12 has one amide group (-CONH-) every 12 carbon atoms. PA6 has one every 6. Amide groups are polar and bond preferentially with water molecules. PA12’s longer chain cuts the concentration of bonding sites by half per unit chain length. The result: PA12 saturates at 3.0% water absorption versus PA66’s 8.5% (ASTM D570, 23°C, Zytel 158L vs 101L). No formulation additive replicates that gap; it is structural. At 50%RH equilibrium, nylon 66 grows 0.6% linearly in dimension; PA12’s lower moisture uptake produces proportionally smaller dimensional shift. That is the engineering reason PA12 costs 2–3x PA66 and the condition under which that premium is justified.

Which nylon grade is best for gears?

Unfilled PA66 is the starting point for most gear applications. Against a steel worm with initial lubrication, Zytel 101 reaches 25 MPa fatigue strength at 10⁶ cycles; with continuous lubrication that rises to 40 MPa (DuPont General Design Principles, page 60). For dry-running gears, MoS2-filled PA66 reduces friction coefficient and extends wear life. The optimal mating pair for friction minimization is one PA66 gear against one POM (Delrin) gear: dynamic CoF 0.08–0.11 at 0.14 MPa and 0.5 m/s, lower than either homogeneous pair (Minlon/Zytel Design Module 2, page 29). PA66 GF30 is not suitable for continuous-contact gears. Maximum surface speed for PA66 against a Zytel worm without lubrication is 0.125 m/s; with initial lubrication against steel this rises to 1.25 m/s.

Related Resources

Nylon Mechanical Properties and Machinability: Tensile Strength, HDT, Moisture Effects, and CNC Parameters — covers detailed CNC parameter ranges, cutting speed and feed rate data for PA6 and PA66, and post-machining stabilization requirements.

Nylon Parts for Engineering Applications: Industry Use Cases, Tolerances, and Procurement Checklist — covers achievable tolerance bands for CNC-machined nylon, industry application breakdowns, and the supplier communication checklist for nylon part orders.

CNC Machining Capabilities — EPOC CRAFTER’s in-stock nylon grades, achievable tolerances, lead times from Asheboro NC and Shenzhen, and the 12-hour quoting process.

Materials and Properties — the full material library including aluminum alloys, stainless steels, and engineering plastics with downloadable grade selection tools.