Glass-filled nylon is a composite material made up of short glass fibers suspended within a nylon matrix
You’ve probably heard of nylon: the synthetic material was developed in the 1930s by DuPont and quickly revolutionized the world of textiles and materials. It even played a role in securing a win for the Allies in the Second World War.  Since then, the material has only grown in terms of its adoption and applications. It has also been improved upon. Composite nylon blends, such as glass-filled nylons are creating new opportunities for nylon-based plastics, particularly for engineering applications. Let’s take a look at glass-filled nylon’s unique properties, its benefits and limitations, and much more.
Glass-filled nylon is a composite material made up of short glass fibers suspended within a nylon matrix. These glass fibers function to reinforce the polymer, increasing its strength and resistance compared to the neat (i.e. unfilled) material. Glass-filled nylon is suitable for injection molding, CNC machining, and has more recently become a popular 3D printing material. Due to its strength and good temperature resistance, the polymer is primarily used for engineering applications.
Before we dive into the specific properties of the composite material, it’s important to first understand its base material, nylon. Nylon is the name for a group of synthetic polyamide plastics typically derived from non-renewable petroleum (though there are efforts to make the material more ecological). 
Nylons are semi-crystalline polymers, which can be tuned to have many different properties and forms: as a fiber it has been used extensively in the production of textiles and garments (famously including nylon stockings); as a film it has been adopted by the food packaging industry ; it can also be made into resin, pelletized or powdered for various other manufacturing processes. Generally speaking, nylon is known for its toughness as well as good temperature and chemical resistance.
The addition of glass enhances nylon’s existing properties and extends the possible applications for the thermoplastic. There are a few different ways of embedding glass into the nylon matrix. With nylon resin, powdered glass particles are mixed into the material; with nylon powder, small spherical glass beads are integrated; and with pellets or filaments, short glass fibers are mixed into the nylon in the extrusion process. It is also possible to control the amount of glass mixed into the nylon base. For instance, 30% glass-filled nylon 66 is a popular blend for extruded nylon.
Recommended reading: Tips and applications for printing with nylon filament
Glass-filled nylons are known for a number of advantageous mechanical, thermal, and chemical properties. Compared to unfilled nylon, these composite blends offer many superior properties, including:
Higher tensile strength
Enhanced creep resistance
Higher fatigue resistance
Superior dimensional stability
Excellent chemical resistance
Good wear resistance
Low coefficient of thermal expansion (i.e. temperature resistance)
Another notable characteristic of glass-filled nylon is that it is an insulator, which opens up applications in the electronics field for housings and other components that require non-conductivity. Nylon is also hygroscopic, meaning that it absorbs water from the environment. Because there are many types of glass-filled nylon, the specific mechanical properties vary. You can consult data sheets to find out the exact properties of different brands of glass-filled nylon.
Like any material, glass-filled nylon has its pros and cons. Here are the key benefits and limitations of the material that can help to inform whether it’s the right choice.
Compared to traditional nylon, glass-filled nylons have a significantly higher tensile strength (as much as 70% higher). Glass-filled nylon components can therefore handle greater loads and stresses. 
Glass reinforcement in nylon dramatically increases the material’s stiffness. Some Nylon GF blends have up to 80% greater stiffness.
Adding glass fibers to nylon reduces the coefficient of thermal expansion, meaning that the material is more resistant to warping and deformation when exposed to temperature changes.
Glass-filled nylon offers greater resistance to creep, which means it is more resistant to deformation under long-term stresses and temperature increases.
The addition of glass fibers or glass particles into nylon does make the resulting composite more brittle than standard nylon. So while glass-filled nylon is resistant to deformation, there is a risk of fracturing under too-high stress.
Embedding glass fibers into nylon makes the material more abrasive. This can cause tools or print heads to wear down at a faster rate than with conventional nylon. Glass-filled nylon parts are therefore also more abrasive, which can wear down adjoining or mated components.
While providing greater strength, glass additives in nylon do make the material heavier. Nylon GF composites can weigh as much as 15% more than unfilled nylon. If lightweighting is a key priority, this can be a disadvantage.
Cost is a final consideration. Due to the additives and additional processing required to make glass-filled nylon, the material is more expensive than its unfilled counterpart.
Glass-filled nylon absorbs moisture and can therefore succumb to structural or dimensional weaknesses if used in humid or wet environments.
Glass-filled nylon is a versatile material that is sold in many different formats to accommodate different production methods. The most common ways to manufacture glass-filled nylon parts are injection molding, machining, and 3D printing.
Plastic injection molding is a widely used method for mass producing plastic products. The process consists of injecting a melted thermoplastic, such as nylon, into a mold cavity under pressure and then rapidly cooling the plastic. The hardened part can then be removed and undergo post-processing if needed. There are many grades of reinforced nylon available for injection molding, the most common of which is glass-filled nylon 66, with a fiber reinforcement ratio of between 10 and 50%.
In the machining process, different types of tools (such as mills, drills, or lathes) are used to remove material from a blank to create precision parts with extremely high tolerances. While it is possible to machine glass-filled nylon, the material does present some challenges. The fibers embedded in the nylon matrix increase abrasion, which can wear down machining tools quickly. For the best results machining glass-filled nylon and other glass-filled polymers, ceramic or carbide tools are preferred over more traditional steel tools. Slower cutting speeds can also improve outcomes. 
There are different 3D printing technologies that can be used to produce glass-filled nylon products, including selective laser sintering (SLS), Multi Jet Fusion (MJF), and Fused deposition modeling (FDM). In the SLS process, layers of powdered material are selectively melted and fused using a laser. With each new layer, the part grows in the print bed. PA 12 is the most common nylon grade for SLS and can be reinforced with up to 40% glass fibers. Nylon 3200 Glass-filled is another engineering thermoplastic for SLS.  There are also glass-filled nylon filaments for FDM 3D printing, the most common of which is nylon 6 (PA 6) with 30% filler. Hardened steel nozzles are recommended when printing nylon GF filaments due to their superior abrasion resistance.
Recommended reading: Selecting the Right Material for 3D Printing
Applications of Glass-Filled Nylon
There are countless applications for glass-filled nylon. The material’s many advantageous properties—including high strength, durability, electrical insulation, and excellent thermal resistance—meet the requirements of many industries, from automotive, to electronics, to consumer goods.
Glass-filled nylon has experienced increased adoption in the automotive sector, which can benefit from the material’s good strength-to-weight ratio. In the automotive industry, weight reduction is a key goal to improve vehicle fuel efficiency: by replacing heavy metal components with the nylon composite, this can be achieved while also reducing costs. Current applications for the material include engine covers, speedometer gears, brake fluid and windshield wiper parts, wire housings and connectors, and more.
Appliance makers and other consumer goods manufacturers, as well as industrial suppliers, are also utilizing reinforced nylons due to their toughness, tensile strength, high-temperature resistance, and other properties.
Here’s a summary of what we covered about glass-filled nylon:
Glass-filled nylon is a composite plastic material consisting of glass fibers or particles suspended within a thermoplastic nylon matrix.
Compared to neat nylon, glass-filled nylon boasts superior tensile strength, rigidity, toughness, chemical resistance, dimensional stability, and thermal resistance.
The abrasive nature of fiber-filled nylon must be taken into account when processing the material: hardened tools and print heads are required.
Glass-filled nylon is increasingly being used as a metal replacement in industries like automotive due to its excellent strength-to-weight ratio.
The material has insulating properties, making it suitable for the production of wire connectors and electrical housings.
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