Heat-Resistant 3D Printing: What Survives Your Temperature

Three numbers get quoted and they mean different things. Getting them straight is most of the work.

• Heat deflection temperature (HDT). The temperature at which a standard test bar bends by a set amount under a set load, per ISO 75 or ASTM D648. Manufacturers publish it at two loads, 0.45 MPa and 1.8 MPa. The 0.45 MPa figure is always higher and is the one marketing quotes. Use the 1.8 MPa figure for anything structural.
• Glass transition temperature (Tg). The temperature at which the amorphous regions of the polymer go from glassy to rubbery. Above Tg a part will creep under sustained load even if it holds shape unloaded. For amorphous polymers like ABS and PC, Tg and HDT are close together. For filled semi-crystalline materials like carbon-fibre nylon they are wildly apart.
• Melting temperature. Effectively irrelevant for design. Nothing useful survives close to it.

One more caveat before the table: these values are measured on injection-moulded or printed test bars in a specific orientation, and a printed part with thin walls and low infill will behave worse than the bar. Treat published HDT as an upper bound, not a guarantee.

Everything below is read off a published manufacturer technical data sheet. Where two manufacturers publish a material, the figures differ, which is itself worth knowing: "PETG" is a family, not a specification.

The useful question is never "what is the strongest heat resistance" but "how hot does this exact spot get." Measure it if you can. A $12 infrared thermometer aimed at the surface on the hottest afternoon of the year will save you a reprint.

Here is the number that catches people out. Bambu Lab's data sheet for PA6-CF lists a heat deflection temperature of 186°C at 0.45 MPa and a glass transition temperature of 68°C. Those look contradictory and they are not.

Carbon fibre reinforcement gives semi-crystalline nylon enormous short-term dimensional stability, which is what the HDT test measures: three minutes of ramping temperature against a fixed load. Sustained load is a different question. Above the glass transition the amorphous phase is rubbery, and a bracket under constant stress will slowly creep over weeks even though it passes a 186°C HDT test.

The practical rule: for a part that carries continuous load, design against the glass transition temperature, not the HDT. For a part that just needs to hold its shape and survive occasional heat spikes, HDT at 0.45 MPa is a reasonable guide.

Nylons have a second complication. Polymaker publishes both dry and moisture-conditioned figures for Fiberon PA6-CF20, and the conditioned tensile strength is roughly half the dry one. Read the conditioning before you use that number: Polymaker's own documentation states its specimens were annealed and then immersed in 60°C water for 48 hours, which is a deliberately aggressive soak rather than anything a part experiences on a shelf. Nylon does take up water and does get weaker and more flexible as it does, but a part left in a workshop lands between those two columns rather than at the bottom. If you order a nylon part, ask whether it will be dried and sealed for shipping.

Heat-treating a printed part after printing increases crystallinity, and for the right polymer that raises the temperature at which it deforms. Polymaker is one of the few manufacturers that publishes before-and-after data, and their HT-PLA sheet is the clearest evidence available:

Material price is only part of the picture, but it is the part people compare first.

The bigger cost is often not the filament. High-temperature materials need an enclosed printer with a heated chamber, a hotend rated above 260°C and, for anything carbon-fibre filled, a hardened steel or ruby nozzle because carbon fibre abrades brass in a few hundred hours. Far fewer makers own that hardware than own a PLA machine, so quotes for PC and nylon jobs carry a scarcity premium on top of material cost.

You can price the material component of your own part with our 3D printing cost calculator, and our full 3D printing cost guide explains how machine time and setup are priced on top of it.

Do not specify the material. Specify the environment and let the maker choose, because they know what their machine can actually run. Include:

• The peak temperature the part will see, measured if possible, and how long it stays there.
• Whether it is under continuous load. This is what decides between designing to HDT and designing to glass transition.
• UV exposure. ABS yellows and goes brittle in sunlight; ASA is the same family formulated to resist it.
• Chemical contact. Cleaning products, fuel and oils rule out some options independently of temperature.
• Dimensional tolerance. ABS, ASA and PC shrink more than PLA, so tight press fits need to be designed with that in mind rather than discovered afterwards.

And be honest about whether you need heat resistance at all. Most parts do not, PLA prints faster and more reliably than anything else here, and paying a polycarbonate premium for a bracket that lives in a spare room is money burned.