DefinitionGlass-filled nylon is a nylon (polyamide) reinforced with short glass fibers, typically PA6 or PA66 with around 20–30% glass by weight.
Explained
What Is Glass-Filled Nylon Made Of?
The base resin is a polyamide. Nylon 66 (PA66) is an important commercial grade, named because its two building blocks each contain six carbon atoms. Nylon 6 (PA6) is the other widely molded grade. Short glass fibers are dispersed through the nylon, and the grade name states the glass content by weight — PA66 GF30 is nylon 66 with 30% glass fiber.
Glass-filled nylon belongs to the wider family of glass-fiber-reinforced plastic (GFRP), which is any plastic reinforced with glass fibers. Polypropylene, for example, is also widely molded in glass-reinforced grades.
Glass fiber generally raises tensile strength, flexural modulus, dimensional stability, wear resistance and heat deflection temperature. Unfilled PA6 and PA66 absorb moisture, lose dimensional stability and have limited strength under demanding conditions. Studies report that 20–30% glass gives the best balance between stiffness and processability.
Unfilled Nylon vs Glass-Filled Nylon
| Property | Unfilled nylon (PA66) | Glass-filled nylon (PA66 GF) |
|---|---|---|
| Tensile strength | ≈51 MPa (7.4 ksi) | ≈111 MPa (16.1 ksi) |
| Elongation at break | ≈292% | ≈8% |
| Stiffness | Lower; flexes under load | Much higher |
| Heat deflection temperature | Lower | Higher |
| Shrinkage | More uniform | Lower along the flow, higher across it |
| Mold wear | Aluminum or P20 tooling | Abrasive; hardened steel such as H13 |
| Typical parts | Gears, bushings, wear parts | Structural brackets, automotive and electronics parts |
Designing and Molding with Glass-Filled Nylon
- Plan for warpage. Fibers align with the melt flow, so the part shrinks less along the flow than across it. Studies on glass-reinforced plastics trace warpage directly to that difference in shrinkage. Gate location, uniform walls and ribs all help.
- Watch weld lines and snap fits. Disordered fiber orientation where flow fronts meet can reduce weld-line strength, and the low elongation makes snap fits prone to cracking. Allow generous radii and check strain at every flexing feature.
- Prototype in the closest material. SLS glass-filled PA12 or machined PA66 can stand in during development, but neither is identical to a molded glass-filled part. Validate the final design in molded material.
Glass is abrasive to mold steel. For high-volume molds and glass-filled or abrasive materials, H13 tool steel is the recommended choice.
Frequently Asked Questions
What is glass-filled nylon? It is nylon, usually PA6 or PA66, reinforced with short glass fibers, typically 20–30% by weight. The fibers raise strength, stiffness and heat deflection temperature compared with unfilled nylon, but reduce elongation at break.
What is glass-fiber-reinforced plastic? GFRP is any plastic reinforced with glass fibers to improve strength and heat resistance. Glass-filled nylon is a common injection-molding example; glass-reinforced polypropylene is another.
What is nylon 66? Nylon 66 (PA66) is a polyamide made from two building blocks that each contain six carbon atoms, which gives it its name. It is an important commercial polyamide and, with nylon 6, a common base resin for glass-filled grades.
Key takeaways
- Glass-filled nylon is PA6 or PA66 reinforced with 20–30% short glass fibers.
- It is much stronger, stiffer and more heat-resistant than unfilled nylon, but far less ductile.
- Fiber alignment during molding creates direction-dependent shrinkage and increases warpage risk.
- Glass fibers are abrasive, so production molds for high volumes should use hardened steels such as H13.
- Prototype in SLS glass-filled PA12 or machined PA66, but validate the final design in molded material.
Example
References
- Polymers: How to Make Nylon — MiraCosta College, Chemistry 102
- Effect of 20 wt% Glass Fiber Reinforcement on the Mechanical Properties and Microstructure of Injection-Molded PA6 and PA66 — Polymers (Basel), 2026;18(3):357
- Shrinkage and Warpage Minimization of Glass-Fiber-Reinforced Polyamide 6 Parts by Microcellular Foam Injection Molding — Polymers (Basel), 2020;12(4):889
- Warpage Reduction of Glass Fiber Reinforced Plastic Using Microcellular Foaming Process Applied Injection Molding — Polymers (Basel), 2019;11(2):360
- Optimizing the Tensile Strength of Weld Lines in Glass Fiber Composite Injection Molding — Materials (Basel), 2024;17(14):3428