Written by Harry S.
Quick answer: Glass fibre makes a filament stiffer and more dimensionally stable, and it is less brittle than carbon fibre. All six OzFDM glass fibre filaments are abrasive, so use a hardened nozzle and dry the roll first. PETG-GF suits workshop parts, ASA-GF outdoor parts, ABS-GF enclosed printers, and PA12-GF or PPA-GF demanding engineering parts.
Glass fibre filaments sit between everyday materials and the carbon fibre engineering range. They print stiffer, flatter parts than the plain polymer, with a matte finish that hides layer lines, but they bring the same hardware demands as carbon fibre: a hardened nozzle, a dry roll and a feed that bypasses the AMS. This guide compares the six glass fibre (GF) filaments we stock using the figures on our product pages, explains how GF differs from carbon fibre (CF), and suggests a pick for common jobs.
What glass fibre adds to a filament
A GF filament is a normal base polymer, such as PETG, ASA or nylon, filled with fine glass fibres. Our product pages describe the same core benefits across the range: improved rigidity, reduced warping and shrinkage, and better dimensional stability than the unfilled material. The ASA-GF page adds that the glass fibre texture gives a matte surface that hides layer lines.
Compared with carbon fibre, glass fibre is not as rigid, but it is significantly less brittle in composites and can stretch further before it breaks. The trade-offs are practical ones. The Prusa Knowledge Base notes that carbon, glass and kevlar fibres are highly abrasive, so a hardened nozzle is necessary, and that the filament itself is more brittle.
Glass fibre improves stiffness and stability, but UV and chemical resistance still come mainly from the base polymer. That is why ASA-GF, not PETG-GF, is the pick for parts that live in the sun.
OzFDM glass fibre filaments at a glance
| Filament | Nozzle | Bed | Speed | Drying | Price (1 kg) |
|---|---|---|---|---|---|
| PETG-GF | 230–260°C | 70–90°C | 40–120 mm/s | 70°C for at least 5 h | $29.95 |
| ABS-GF | 220–240°C | 100–110°C | 40–60 mm/s | 80°C for 5 h | $31.95 |
| ASA-GF | 240–260°C (250°C recommended) | 100–120°C (110°C recommended) | 40–250 mm/s | 80°C for at least 5 h | $39.95 |
| PET-GF | Not yet published | Not yet published | Not yet published | Not yet published | $62.95 |
| PA12-GF | 260–280°C | 60–100°C | Not yet published | 80°C for about 12 h | $139.95 |
| PPA-GF | Not yet published | Not yet published | Not yet published | Dry thoroughly and feed from a heated dry box | $129.95 |
These settings come from our product pages at the time of writing. PET-GF, PA12-GF and PPA-GF are recent additions, and their pages say full technical specifications are still being finalised, so check the product page for updated figures before you print.
Stiffness and heat: what the data shows
At the time of writing, ASA-GF is the only glass fibre filament in our range with a full data sheet, and its numbers show something every GF user should know: the part is far stronger along the layers than across them.
| ASA-GF property | Along the layers (X-Y) | Across the layers (X-Z) |
|---|---|---|
| Flexural strength (ISO 178) | 72.5–74.1 MPa | 27.2–31.7 MPa |
| Flexural modulus (ISO 178) | 3359–3368 MPa | 1359–1590 MPa |
| Impact strength (ISO 180) | 6.3–6.9 kJ/m² | 2.5–3.2 kJ/m² |
| Tensile strength (ISO 527) | 40.8–41.3 MPa | Not listed |
Across the layers, ASA-GF keeps well under half of its flexural strength. Orient brackets and clips so the main load runs along the printed lines, not across the layer bonds. The same data sheet lists a heat deflection temperature of 88°C at 0.455 MPa and a continuous use temperature of 85°C.
The PETG-GF and ABS-GF pages say mechanical and thermal data will be added once testing is complete, and the newer GF lines have no published HDT yet. When comparing any two filaments, check that the figures use the same test and load. Our heat deflection temperature chart collects the values that are published.
Glass fibre vs carbon fibre
| Factor | Glass fibre (GF) | Carbon fibre (CF) |
|---|---|---|
| Stiffness | Less rigid than carbon fibre | More rigid |
| Toughness | Less brittle, stretches further before breaking | More brittle |
| Electrical | Glass fibre has low electrical conductivity | Some grades have low resistance: our PA12-CF lists surface resistance of ≤10² Ω and PPA-CF ≤10³ Ω |
| Surface | Matte, hides layer lines | Matte with a subtle grain texture |
| Colours at OzFDM | Natural and black; natural suits painting | Mostly black, with colours in PETG-CF and ASA-CF |
| Nozzle wear | Abrasive, hardened nozzle needed | Abrasive, hardened nozzle needed |
Glass fibre is the cheaper raw material, but in our range the GF and CF versions of the same base polymer are priced close together, so choose on properties rather than price.
| Base polymer | GF version | CF version |
|---|---|---|
| PETG | PETG-GF $29.95 | PETG-CF $39.95 |
| ASA | ASA-GF $39.95 | ASA-CF $38.95 |
| PET | PET-GF $62.95 | PET-CF $64.95 |
| PA12 | PA12-GF $139.95 | PA12-CF $159.95 |
| PPA | PPA-GF $129.95 | PPA-CF $129.95 |
Pick GF when a part needs to flex a little without cracking, when you would rather avoid a conductive filler, or when it will be painted. Pick CF when maximum stiffness matters most, such as the drone components our PETG-CF page mentions.
Hardware you need
A hardened nozzle
Treat every GF filament as abrasive. The ASA-GF and PA12-GF pages recommend a hardened steel nozzle, the PET-GF page warns that glass fibre may quickly wear standard brass nozzles, and the PPA-GF page recommends hardened steel or ruby. Prusa lists 0.4 mm nozzles and 0.2 mm layers as the lowest optimal values for fibre-filled filament. Our comparison of ruby, tungsten and steel nozzles covers the options.
An enclosure for ABS-GF, ASA-GF and the nylons
The ABS-GF, ASA-GF and PA12-GF pages all say the material performs best in an enclosed printer with stable heat, which the pages link to cleaner layer bonding and less warping on larger models. PPA-GF needs a high-temperature setup. The PETG-GF and PET-GF pages do not call for an enclosure, and PET-GF is described as easier to print than many advanced engineering materials.
Feeding and the AMS
- PETG-GF: the product page says to feed it from an external spool holder rather than the AMS.
- ABS-GF and ASA-GF: both pages say the same, an external spool holder or sealed dry box straight into the printer.
- PET-GF: manual loading from an external spool holder or dry box is recommended, and the AMS Lite is generally not recommended for third-party glass fibre filament.
- PA12-GF: manual loading or a compatible dry box, because the filament must stay dry while printing.
- PPA-GF: generally not recommended for standard AMS systems; feed it directly from a heated dry box.
Drying and storage
Damp filament causes bubbling, uneven extrusion and rough surfaces, and the nylon-based grades are the most sensitive. The PA12-GF page warns that humidity affects surface quality, layer bonding and extrusion consistency, and the PPA-GF page describes its polyphthalamide base as highly hygroscopic. Dry every roll at the temperature in the table above before printing, then store it in an airtight bag or container with desiccant. Our vacuum storage range and the filament storage and drying guide cover the details.
Which glass fibre filament for which job
| Job | Pick | Why |
|---|---|---|
| Tool holders, garage organisers, jigs | PETG-GF | Rigid with low warping, handles warm and semi-outdoor spots, and the lowest price in the range |
| Outdoor brackets, panels and protective covers | ASA-GF | ASA's UV resistance plus glass fibre stiffness, with an 88°C HDT |
| Functional prototypes and automotive fixtures | ABS-GF | Stiff and dimensionally stable in an enclosed printer; natural is easy to paint |
| Housings and fixtures that need more stiffness than PETG | PET-GF | Glass-reinforced PET with chemical resistance and reduced warping |
| Tough nylon tooling, brackets and housings | PA12-GF | PA12 toughness and chemical resistance with added rigidity |
| Load-bearing parts near heat, automotive fluids or solvents | PPA-GF | Polyphthalamide base for heat and chemical resistance |
Shop the materials in this guide
- Glass Fibre Filament: the full GF range in one place.
- 1.75 mm PETG-GF Filament - 1 KG: the easiest entry into glass fibre.
- 1.75 mm ASA-GF Filament - 1 KG: weather-resistant GF with a full data sheet.
- 1.75 mm PET-GF Filament - 1 KG: a stiffer step up from PETG.
- 1.75 mm PA12-GF Filament - 1 KG: glass-reinforced nylon for tough functional parts.
- 1.75 mm PPA-GF Filament - 1 KG: for heat and chemical exposure.
Frequently asked questions
Do I need a hardened nozzle for PETG-GF?
Yes. Glass fibres are highly abrasive whatever the base polymer, and a brass nozzle will wear. Fit a hardened steel nozzle of 0.4 mm or larger before you load any GF filament.
Is glass fibre filament stronger than carbon fibre filament?
It depends on what you mean by strong. Carbon fibre is more rigid, while glass fibre is less brittle and stretches further before breaking. The base polymer matters more than the fibre for UV and chemical resistance, so compare the data sheets for the exact products.
Can I print glass fibre filament from an AMS?
We would not. Every glass fibre page in our range now recommends feeding from an external spool holder or a dry box instead. Bambu Lab's own filament guide warns that third-party carbon and glass fibre filament can be hard and rough enough to damage the AMS or AMS lite channel, or brittle enough to break inside it, and a direct feed keeps the abrasive fibres away from the AMS gears and tubing.
Why did my glass fibre part snap along a layer line?
Layer bonds are the weak direction. ASA-GF data shows flexural strength of 72.5–74.1 MPa along the layers but only 27.2–31.7 MPa across them. Reorient the part so loads run along the printed lines, and make sure the filament was dry.
How long should I dry glass fibre filament?
Follow the product page: 70°C for at least 5 hours for PETG-GF, 80°C for 5 hours for ABS-GF, 80°C for at least 5 hours for ASA-GF, and 80°C for about 12 hours for PA12-GF. PPA-GF should be thoroughly dried and printed from a heated dry box.
