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Should I use unfilled or glass-filled nylon 66?
Use PA66-GF30 for structural brackets, housings and metal replacement: 30% glass roughly doubles tensile strength, to about 28,000 psi (190 MPa) from 12,000 psi (83 MPa) dry, triples stiffness, and lifts heat deflection near 480 °F (250 °C). Use unfilled nylon 66 for gears, bushings, clips and snap fits, where toughness, gentle wear on mating parts and a smooth surface matter more.
Nylon 66 (PA66)
Nylon 66, 30% glass-filled (PA66-GF30)
By the numbers
Priced on the same representative part: housing, injection molding, 10,000 pcs.
Tensile strengthMPa
PA66
83
PA66-GF30
190
Densityg/cm³
PA66
1.14
PA66-GF30
1.37
Max service temp°C
PA66
100
PA66-GF30
120
Raw material cost$/kg
PA66
3.8
PA66-GF30
4
Which should you pick?
Pick PA66 when
- Snap fits and clips need high strain before breaking
- Sliding parts such as gears, bushings and rollers run against other parts
- Cosmetic surfaces need a smooth finish
- Lower mold wear and tool cost matter
Pick PA66-GF30 when
- The part replaces a die cast aluminum or zinc bracket
- Stiffness must hold under load at temperature
- Sustained loads make creep a concern
- It is a heat-stabilized under-hood part
Key differences
| PA66 | PA66-GF30 | |
|---|---|---|
| Shrink | About 1.5–2%, similar in all directions | 0.3–0.5% along flow, 0.8–1.2% across flow |
| Warp risk | Controlled with uniform walls | Anisotropic; needs balanced gating and ribs aligned with flow |
| Surface | Smooth and glossy | Fiber-streaked; texture cosmetic faces |
| Mold steel | Standard P20 or H13 | Hardened tool steel; glass is abrasive |
| Weld line strength | Small loss | Can lose up to about half |
| Wear on mating parts | Gentle on shafts and mating plastics | Glass abrades mating surfaces |
| Snap-fit design | Tolerates higher strain | About 3% elongation; design low-strain snaps |
Questions
How much stronger is glass-filled nylon?
30% glass roughly doubles tensile strength, 190 versus 83 MPa dry, and triples stiffness to about 1.45 million psi (10 GPa). It cuts elongation to about 3%, so parts are stronger but less forgiving of snap-fit strain.
Why do glass-filled nylon parts warp?
Fibers align with flow, so shrink along the flow, about 0.3–0.5%, is lower than across it, about 0.8–1.2%. Uneven walls and one-sided gating magnify the difference. Uniform walls, balanced gating and ribs aligned with flow reduce warp.
Can glass-filled nylon replace a die casting?
Often, for brackets, housings and covers under moderate load. It is about half the density of aluminum, needs no finishing, and molds in features. Metal stays the better call above about 300 °F (150 °C) under load, for tight long-term tolerances, or for high sustained loads.
Does glass-filled nylon absorb water?
Yes, but less than unfilled nylon, because glass replaces 30% of the resin and the fibers restrain swelling. Still design with conditioned properties for humid service.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.