Nylon 6/6 (30% Glass-Filled) vs Nylon 66 (PA66)
Nylon 6/6 with 30% glass fill and unfilled Nylon 66 (PA66) share the same base polymer, but the glass reinforcement transforms its mechanical profile. The filled grade more than doubles tensile strength (~170 vs ~83 MPa), greatly raises stiffness, heat-deflection temperature (~120 vs ~100 C), and dimensional stability. The trade-off is a large loss of toughness and elongation (~3% vs ~60%), making it stiff but more brittle.
The verdict
Choose Nylon 6/6 30% glass-filled for stiff, strong, dimensionally stable structural parts and gears that run hotter and hold tolerances. Choose unfilled Nylon 66 when toughness, impact resistance, and flexibility matter more than rigidity, for bushings and wear parts that must absorb shock.
Side-by-side data
| Property | Nylon 6/6 (30% Glass-Filled) | Nylon 66 (PA66) |
|---|---|---|
| Category | Engineering Plastic | Engineering Plastic |
| Density (g/cm³) | 1.37 | 1.14 |
| Tensile strength (MPa) | 170 | 83 |
| Yield strength (MPa) | 170 | 80 |
| Elongation (%) | 3 | 60 |
| Hardness | M93 | R120 |
| Max service temp (°C) | 120 | 100 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 0.25 | 0.25 |
| Typically used for | Stiff structural housings & gears | Gears, bushings & wear parts |
Which should you choose?
Choose Nylon 6/6 30% Glass-Filled when…
- High stiffness and strength are needed — tensile ~170 vs ~83 MPa for unfilled
- Higher heat-deflection and service temperature help (~120 C vs ~100 C)
- Dimensional stability matters; glass fill reduces moisture-driven movement and warping
- The part is a stiff structural housing or load-bearing gear
- Lower creep under sustained load is required
- Reduced thermal expansion improves tolerance control
Choose Nylon 66 (PA66) when…
- Toughness and impact resistance lead — elongation ~60% vs ~3% for filled
- The part must flex or absorb shock without cracking
- Lower cost is preferred (~1.5 vs ~2.0)
- A smoother, less abrasive surface is needed for sliding wear parts
- Easier machining matters (3.5 vs 3.0 for filled)
- Brittleness from glass fill would be a liability
Key differences that matter
- Glass fill more than doubles tensile strength (~170 vs ~83 MPa) and greatly increases stiffness
- Filled nylon raises heat-deflection/service temperature (~120 vs ~100 C) and improves dimensional stability
- The major trade-off is toughness: elongation drops to ~3% from ~60%, making filled nylon more brittle
- Glass fill reduces creep and thermal expansion, helping tolerance control under load and heat
- Filled nylon is denser (1.37 vs 1.14) and more abrasive to machine (3.0 vs 3.5)
- Unfilled PA66 is tougher, cheaper (~1.5 vs ~2.0), and better for shock-loaded sliding wear parts
- Both share the same PA66 chemistry and moisture-absorption character
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Open the Material SelectorGet a Quote →Frequently asked questions
What does 30% glass fill do to nylon 66?
It dramatically raises stiffness and strength — tensile jumps from about 83 to 170 MPa — and improves heat-deflection temperature (~120 vs ~100 C), creep resistance, and dimensional stability. The cost is toughness: elongation falls from about 60% to 3%, so the filled grade is rigid and strong but brittle, fracturing rather than bending under impact.
When is unfilled nylon 66 the better choice?
When toughness, impact resistance, or flexibility matter more than rigidity. Unfilled PA66's ~60% elongation lets it absorb shock and flex without cracking, suiting bushings and sliding wear parts. It is also cheaper (~1.5 vs ~2.0), machines more easily, and presents a smoother, less abrasive surface. For shock-loaded or flexing parts, unfilled wins.
Does glass fill change machinability?
Yes, for the worse. The glass fibers are abrasive and wear cutting tools faster, dropping machinability to about 3.0 versus 3.5 for unfilled, and they can leave a rougher surface. Filled nylon is most often injection molded to near-net shape; when machining is needed, expect more tool wear and dust than with unfilled PA66.
Do both absorb moisture?
Yes — both share the PA66 base and absorb moisture, which can swell parts and shift dimensions. Glass fill reduces the dimensional effect somewhat because the rigid fibers restrain movement, improving stability over the unfilled grade. But neither is moisture-free; for the most dimensionally stable dry-running parts, a lower-absorption material like POM/Delrin may be preferable.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.