PA-GF High-temperature glass-fiber nylon (QIDI PAHT-GF, also sold as PPA-GF)

PA-GF is a high-temperature nylon reinforced with chopped glass fiber. The grade we print is QIDI PAHT-GF, also sold as PPA-GF: a PPA (polyphthalamide) base, a semi-aromatic polyamide whose stiff ring structures give higher heat resistance and lower moisture uptake than ordinary nylon. It's the glass-fiber sibling of PAHT-CF, printed at the same temperatures and benefitting from the same annealing.

Glass-filled nylon is one of the most widely used engineering plastics in molded products, from power-tool housings to automotive brackets, so many engineers know how it behaves. Printed PA-GF brings much of that character: strong, reasonably stiff, heat resistant once annealed, and with good wear resistance, which QIDI markets along with self-lubricating properties.

Glass fiber versus carbon fiber is the key choice here. Glass is electrically non-conductive, generally cheaper as a reinforcement and less stiff than carbon. In molded plastics, glass-filled grades are usually considered tougher, but QIDI's own impact figure for PAHT-GF is lower than its PAHT-CF figure, so don't assume printed PA-GF is more impact resistant without testing. It also looks different: a lighter, less uniform matte finish rather than carbon's deep black.

Like other fiber-filled filaments, PA-GF is abrasive and needs a hardened nozzle of at least 0.4 mm; QIDI says the 0.2 mm nozzle is not compatible. QIDI also notes that short glass fiber makes the filament itself more brittle on the spool, which is one reason we keep it on a short, dry feed path from a sealed dry box rather than in the QIDI Box.

PA-GF is strong. QIDI's product page lists tensile strength of 86.49 and 90.50 MPa and bending strength of 137.78 and 140.77 MPa; the page doesn't label the two values, but they appear to be unannealed and annealed. Its guide lists bending strength of 140.77 MPa in XY, matching the higher figure.

It's stiff but less so than carbon fiber. Bending modulus is 4135.14 to 4897.64 MPa, compared with 6727.22 MPa for PAHT-CF as printed. In practice a PA-GF bracket will deflect more under the same load than a PAHT-CF one, which can be an advantage where some give helps spread load.

QIDI's impact strength for PAHT-GF is 7.29 kJ/m², lower than PAHT-CF's 10.37 kJ/m², and elongation at break is 1.78%. That impact figure is identical to the one on QIDI's UltraPA-CF25 page, which may be a copy error, so treat it with caution. Either way, PA-GF is not a ductile material: overload breaks it rather than bending it.

Anisotropy, meaning properties that depend on direction, applies here as with all fiber-filled prints. QIDI's guide lists Z tensile strength of 59.58 MPa, the best layer bonding of the fiber nylons in its table, but still well below in-plane strength. Fibers align along printed lines, so we orient parts to keep loads along layers and toolpaths.

HDT, the heat deflection temperature, is the temperature at which a test bar bends a set amount under a fixed load. QIDI's product page lists 80 °C as printed (load and condition not stated), and its comparison data lists 180.0 °C at 0.45 MPa after annealing. No 1.80 MPa (heavier-load) value is published for PA-GF, so expect a much lower figure under heavy load, as with PAHT-CF.

So annealing is what unlocks PA-GF's heat resistance. As printed, it handles heat about like PETG. Annealed, it is in the same high-heat class as PAHT-CF at light load. The melting point of 237 °C is the absolute ceiling, and parts should stay well below it.

QIDI's guide specifies annealing at 100 °C for 8 hours; the product page says 80–100 °C for 4–8 hours. Glass fiber limits shrinkage, but annealed parts can still change size slightly or distort, so we anneal only by agreement and measure a test piece first.

Glass fiber doesn't block UV the way carbon black does, so PA-GF's UV performance depends on its pigment. Expect slow yellowing or fading and some chalking in long-term sun, and plan on a coating for cosmetic outdoor parts.

QIDI lists saturated water absorption of 1.75%, between PAHT-CF and PA12-CF, so outdoor parts take on some moisture in wet weather and lose a little stiffness.

PA-GF generally resists oils, greases, fuels and many solvents, like other nylons, and PPA-based nylons are generally more resistant to hot water and automotive fluids than PA6. Glass fiber itself is chemically inert in most environments.

Strong acids and strong oxidizers generally attack polyamides. If your part will be exposed to a specific chemical, especially when hot, tell us and test a sample.

PA-GF must be printed dry. Like all nylons, it's hygroscopic, meaning it pulls water from the air, and wet filament prints with bubbles, stringing and weak layers. We dry it at 80–100 °C and print from sealed storage below 15% RH, as QIDI requires.

After printing, parts absorb some moisture over time. QIDI's wiki, quoted in its PAHT-CF guide, says nylon parts in humid air or water gradually lose some strength and stiffness and become tougher. Expect the same trend here, with slight dimensional growth in humid conditions.

PA-GF prints with a matte, slightly textured surface. Compared with carbon fiber's uniform deep black, glass-filled parts are usually lighter in color and can show a faint sparkle or fiber texture at certain angles.

Layer lines are moderately hidden. Supported surfaces are rougher than top surfaces, and very small details are softened by the 0.4 mm minimum nozzle.

Annealing is the main post-process and is done only by agreement. PA-GF drills, reams and taps reasonably well, and heat-set inserts install cleanly. Glass fiber is very abrasive to tools, so expect faster wear on drills and taps than with unfilled plastics.

Sanding exposes glass fibers, which can be itchy and irritating; wear gloves and a mask. Vapor smoothing isn't something we offer for this material. Painting is possible with suitable primers.

Glass fiber limits shrinkage and warping, and QIDI claims no warping and shrinkage in printing. Large flat parts print far more reliably than with unfilled nylon. Annealing can shift dimensions slightly, so finish critical fits afterward or test first.

Holes print slightly undersized, as with all FDM parts. Design precise holes undersized and ream them to size; vertical holes are more accurate than horizontal ones.

Moisture changes dimensions slightly after printing, a little less than with PA12-CF given its lower water absorption. For precision fits, tell us the tolerance you need, and we'll advise whether to ream after annealing or condition the part in room air before measuring.