PA6 (Nylon 6) vs PA66 (Nylon 66) Injection Molding: Properties, GF30 & Cost Guide

Nylon 6 (PA6) and Nylon 66 (PA66) together account for over 85% of global polyamide injection molding, yet engineers frequently default to PA66 (Zytel 101L, Ultramid A3) out of habit—paying a 10% to 25% resin price premium and suffering rough “floating glass fiber” surfaces on parts where PA6 (Ultramid B3, Durethan B30S) would perform better.

Conversely, substituting PA6 into an under-hood bracket or high-voltage relay engineered for PA66 drops the crystalline melting point by 40 °C (220 °C vs 260 °C), increases equilibrium moisture swell by 15%–25%, and lengthens press cooling cycles by 10%–20%. Use this side-by-side comparison matrix—covering both unfilled and 30% glass-fiber reinforced (GF30) grades—to specify the right polyamide on your part print.

1. Master Engineering Matrix: Unfilled & 30% Glass-Filled PA6 vs PA66

Because mechanical properties of both polyamides shift dramatically between the Dry-As-Molded (DAM, ~0.1% moisture) state and the Conditioned (50% RH, 23 °C equilibrium) state, both values are listed below:

Property / Processing Metric	Unfilled PA6 (Nylon 6)	Unfilled PA66 (Nylon 6/6)	30% Glass-Filled PA6 (PA6-GF30)	30% Glass-Filled PA66 (PA66-GF30)
Monomer Chemistry	Ring-opening polymerization of Caprolactam (6 carbons)	Polycondensation of Hexamethylenediamine + Adipic Acid (6,6 carbons)	PA6 + 30 wt% chopped E-glass	PA66 + 30 wt% chopped E-glass
Crystalline Melting Point ($T_m$)	220 °C (428 °F)	260 °C (500 °F — +40 °C higher!)	220 °C (428 °F)	260 °C (500 °F)
Heat Deflection Temp (HDT @ 1.8 MPa)	65 – 75 °C	75 – 90 °C	200 – 210 °C	245 – 255 °C (survives peak engine-bay heat)
Tensile Strength (DAM / 50% RH)	80 MPa / 45 MPa	85 MPa / 55 MPa	180 MPa / 115 MPa	205 MPa / 140 MPa
Flexural Modulus (DAM / 50% RH)	2.8 GPa / 1.1 GPa	3.1 GPa / 1.4 GPa	8.5 GPa / 5.5 GPa	9.2 GPa / 6.5 GPa
Notched Izod Impact (DAM / 50% RH)	60 J/m / 220+ J/m	50 J/m / 140 J/m	115 J/m / 160 J/m	100 J/m / 130 J/m
Moisture Absorption (23 °C / 50% RH Air)	2.7% – 3.0% (9.5% in water)	2.3% – 2.6% (8.5% in water)	1.8% – 2.0% (6.0% in water)	1.5% – 1.7% (5.5% in water)
Linear Dimensional Swell (DAM to 50% RH)	+0.55% to +0.70%	+0.25% to +0.40%	+0.15% to +0.25%	+0.10% to +0.15%
Mold Shrinkage (Flow / Cross-Flow)	1.0% – 1.4% (lower than PA66)	1.3% – 1.8% (higher crystallinity)	0.3% Flow / 0.85% Cross	0.35% Flow / 1.0% Cross
As-Molded Surface Cosmetics	High Gloss & Smooth (slower crystallization hides glass fibers)	Matte / Prone to Silver Floating Glass Fibers in GF30	Class A Exterior Capable (power tools, mirror housings)	Industrial Structural Finish (brackets, manifolds)
Press Cycle Time	Baseline (1.00x)	10% – 20% Faster (0.82x–0.90x — freezes at higher temp)	Baseline (1.00x)	10% – 15% Faster
Relative Resin Cost (per kg)	1.00x (Lowest)	1.12x – 1.28x (adiponitrile feedstock volatility)	1.00x	1.10x – 1.25x

2. Four Practical Scenarios: When to Choose PA6 vs When to Choose PA66

Scenario 1: Exterior Housings with 30% Glass Fiber (PA6-GF30 Wins)

Why are cordless power-tool housings (DeWalt, Milwaukee, Bosch), lawnmower decks, automotive side-mirror brackets, and office-chair bases almost universally molded in PA6-GF30 rather than PA66-GF30?

• The Crystallization Speed Secret: PA66 freezes (crystallizes) rapidly at ~225–235 °C as soon as the melt touches the steel mold wall, trapping white glass fibers right on the visible skin (floating fibers / silver frosting).
• PA6 crystallizes more slowly and at ~180–190 °C: That extra fraction of a second allows a resin-rich polymer skin to wet out smoothly against the cavity steel before solidifying—producing a uniform, high-gloss, fiber-free Class A surface at a lower mold temperature (80–95 °C vs 100–120 °C for PA66) while delivering 15%–20% higher drop-impact toughness and 10%–20% lower resin cost.

Scenario 2: Under-Hood Automotive & High-Heat (> 180 °C) Components (PA66-GF30 Wins)

When a part sits inside an automotive engine bay, near an exhaust manifold, or inside an industrial motor housing exposed to 160–220 °C peak temperatures and hot glycol/engine oil:

• PA6-GF30 softens as temperatures approach its 205 °C HDT and 220 °C melting point.
• PA66-GF30 holds an HDT of 245–255 °C (40–45 °C higher than PA6-GF30), exhibits lower thermal creep under bolt torque, and resists hot radiator glycol (50/50 water-ethylene glycol at 130 °C) longer before hydrolytic cracking.

Scenario 3: High-Volume Fast-Cycling Cable Ties, Clips & Connectors (Unfilled PA66 Wins)

Why are billions of electrical cable ties (zip ties), PCB standoffs, and automotive wire-harness connectors molded from unfilled PA66 (Zytel 101L)?

• Because PA66 solidifies at a 40 °C higher temperature and crystallizes faster than PA6, thin-wall parts can be ejected from the mold 1.5 to 3.0 seconds earlier per shot. Over a 10-second multi-cavity cycle, saving 2.0 seconds cuts press machine-hour cost by 20%, easily paying back the higher raw-material price of PA66.

Scenario 4: Cold-Impact Ductility & Thick-Section Gears (PA6 Wins)

In thick-walled rollers, caster wheels, or snap-fit clips that must flex without snapping in dry warehouse air, PA6 offers higher elongation and notched impact strength (60 J/m DAM and 220+ J/m conditioned) and slightly lower mold shrinkage (1.0%–1.4% vs 1.3%–1.8% for PA66), reducing the risk of internal shrinkage voids.

3. Can You Substitute PA6 for PA66 in an Existing Injection Mold?

During adiponitrile (PA66 feedstock) supply shortages or cost-reduction initiatives, buyers frequently ask whether they can drop PA6 into an existing PA66 production tool:

1. In 30% Glass-Filled Tools (PA66-GF30 $\rightarrow$ PA6-GF30) — Usually YES: Because the 30% glass-fiber skeleton dominates shrinkage in both resins (0.25%–0.35% flow shrinkage), switching a PA66-GF30 tool to PA6-GF30 (or a PA66/PA6 copolymer blend like Ultramid A3WG6 / B3WG6) typically shifts dimensions by less than ±0.001 mm/mm (0.1%), which the molder can dial in via holding pressure—provided the application temperature stays below 170–180 °C.
2. In Unfilled Tools (Unfilled PA66 $\rightarrow$ Unfilled PA6) — Caution on Tight Tolerances!: Unfilled PA6 shrinks 0.2% to 0.4% less in the mold (1.2% vs 1.5% for PA66), meaning a part molded in a PA66-shrunk cavity will come out +0.2% to +0.4% larger immediately after molding—and will then grow an extra +0.2% larger once conditioned in humid air! Verify whether mating bores can absorb +0.003–0.005 mm/mm before approving an unfilled substitution.

Buyer FAQs

What is the main difference between PA6 and PA66 in injection molding?

PA66 (Nylon 66) has a 40 °C higher melting point (260 °C vs 220 °C), 10%–15% higher stiffness and tensile strength, 15%–20% lower moisture absorption (2.5% vs 2.9% at 50% RH), and 10%–20% faster cycle times due to rapid crystallization. PA6 (Nylon 6) costs 10%–25% less per kg, offers 20%–35% higher impact toughness, processes at lower barrel temperatures (240–270 °C vs 275–295 °C), and produces a dramatically smoother, high-gloss surface finish in glass-filled grades (PA6-GF30).

Which is better for 30% glass-filled parts: PA6-GF30 or PA66-GF30?

Choose PA6-GF30 for visible external housings, power-tool bodies, furniture frames, and impact-exposed brackets operating below 170 °C—its slower crystallization encapsulates glass fibers beneath a smooth resin skin (avoiding white “floating fibers”) while providing higher impact strength and lower resin cost. Choose PA66-GF30 for under-hood automotive components, hot cooling manifolds, and high-load structural brackets operating between 170 °C and 240 °C where maximum thermal creep resistance is mandatory.

Which absorbs more water: Nylon 6 (PA6) or Nylon 66 (PA66)?

Nylon 6 (PA6) absorbs more moisture than Nylon 66: at standard 23 °C / 50% RH ambient equilibrium, unfilled PA6 absorbs 2.7%–3.0% moisture (9.5% when submerged in water) and grows linearly by +0.55%–0.70%, whereas unfilled PA66 absorbs 2.3%–2.6% moisture (8.5% submerged) and grows by +0.25%–0.40%. Adding 30% glass fiber cuts moisture absorption and dimensional swell roughly in half for both grades.

Can PA6 and PA66 be mixed or ultrasonically welded together?

While specialized PA66/PA6 copolymer blends are compounded at the resin factory to combine PA6’s surface finish with PA66’s heat resistance, molders should not randomly dry-blend PA6 and PA66 pellets in the press hopper, nor can a molded PA6 part be reliably ultrasonically welded to a PA66 part because their crystalline melting points differ by 40 °C (220 °C vs 260 °C).

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, sell materials, or certify suppliers. Polyamide mechanical properties depend heavily on moisture conditioning (Dry-As-Molded vs 50% RH ISO 1110); always specify the inspection conditioning state on your engineering drawing.