Printed parts softening in heat: hot cars and sun

This guide is for anyone whose finished print has bent, drooped or warped since it came off the printer: a phone mount on a dashboard, a bracket by a sunny window, a part near a heater. It sets out what each filament maker publishes about heat for PLA, PETG, ABS, ASA, PC and carbon-fiber nylon, where makers document annealing, and how to pick a material for the next print. Make sure you're in the right place:

We haven't found a filament maker that publishes car interior temperatures, so this page doesn't give one. Use the highest temperature you know the part will see, and compare it with the maker figures below.

What do the makers say about heat?

Before the data sheets, here's what makers say about each material in their guides and product pages.

Most of these statements don't say how the number was measured. The data sheets below do, and that's what makes them comparable.

How do you read a heat figure?

Data sheets give two kinds of heat number:

• HDT (heat deflection temperature), tested to ISO 75 at a stated load. The sheets here give it at 1.8 MPa, 0.45 MPa, or both.
• Vicat softening temperature, tested to ISO 306 (Bambu Lab and Polymaker also cite GB/T 1633).

These are different tests, and the same material gets different HDT numbers at the two loads. So only compare like with like: the same test, the same load, ideally from the same maker. Bambu Lab's data sheets add that the values "are for design reference and comparison only," and that a printed model's performance "is related to many other factors, including printers, printing conditions, printing models, printing parameters, etc."

Bambu Lab's figures

All from Bambu Lab's own data sheets. HDT is ISO 75. Vicat is ISO 306 / GB/T 1633.

How the specimens were treated matters. The PLA Basic sheet says all specimens "were annealed and dried at 55 °C for 8 h before testing." The ABS, ASA, PC and PAHT-CF sheets say 80 °C for 12 hours. The PETG Basic sheet lists the print settings for its specimens and doesn't say they were annealed.

The PC sheet is the odd one out: its 1.8 MPa figure is higher than its 0.45 MPa figure, the reverse of every other sheet on this page. We've reported it as printed.

Polymaker's figures

All from Polymaker's data sheets. HDT is ISO 75. Vicat is ISO 306 / GB/T 1633.

The Polymaker ASA sheet notes that its figures are based on testing with PolyLite ASA (SKU PF01046). The Fiberon PA6-CF20 sheet recommends annealing the model "in the oven at 100°C for 16 hours" after printing, and notes that its mechanical test specimens were annealed that way. It gives one set of heat figures, not an as-printed set alongside.

Polymaker's general material pages give different, rounder numbers. Its ASA page gives 86–96 °C HDT at 1.8 MPa for ASA and, in an ASA vs ABS table, 100–110 °C HDT for ABS (no load stated). Its PC page gives HDT "exceeding 115°C" for PC. The ASA and PC figures don't match its own data sheets above, and the ABS range only touches the PolyLite ABS sheet's 0.45 MPa figure. Go by the data sheet for the spool you buy.

Prusament's figures

From Prusa Polymers' data sheets. HDT is ISO 75.

The "Temperature resistance" figures on the Prusament PETG, ASA, PC Blend and PC Blend Carbon Fiber pages (68, 93, 113 and 114 °C) are the same numbers as each data sheet's 0.45 MPa HDT. The Prusament PLA page gives 55 °C without naming a test, and its data sheet lists the same 55 °C at both loads.

Prusa's own pages don't agree on PETG. The Prusament PETG page says 68 °C, while Prusa's PETG guide says "most exterior use (with temperatures below 80 °C)." If heat matters, design to the lower number.

Thickness and load matter, not just the material

Polymaker's wiki says "The heat resistance of a printed object cannot be determined by material rating alone." It says "Thin-walled or low-density prints are more prone to warping and deformation when exposed to heat," while "Thicker, denser parts" are "more resistant to softening and warping during exposure." Its example: "A thin tray and a solid block made of the same filament can show very different behaviors when placed under heat."

Polymaker's HT-PLA page shows how much the test conditions change the picture. It says HT-PLA keeps "its shape at high temperatures (up to 130°C) without sagging or deforming under its own weight." The same page lists an as-printed HDT of 58.6 °C at 1.8 MPa. Both are maker figures. One is a part carrying only its own weight, the other a test bar under a stated ISO 75 load. A part that also has to hold something, such as a phone in a mount, isn't covered by the no-load claim.

So if a part failed in heat, think about what it was doing. A thin wall or a part under load may need a bigger margin than the data sheet's number suggests, or a thicker design.

Sun: heat and UV are separate claims

Makers talk about sunlight mainly in terms of UV, not heat:

• PLA: Prusa says PLA "degrades under UV light." Prusament says the combination of "low UV resistance" and "low-temperature resistance" means it's "not ideal for outdoor use."
• ASA: Prusa calls ASA "suitable for outdoor use, due to its high UV light and temperature resistance." Polymaker says ASA "Retains color and strength under prolonged sun exposure."
• PC: Polymaker's PC page lists "UV Sensitivity: Degrades under prolonged sunlight unless coated."
• Specialty PLA: Polymaker says its Matte PLA for Production "performs on par with ASA" in weather resistance testing. That's a weathering claim. It doesn't change the PLA heat figures above.

A part in the sun has to cope with both. If it also gets hot, the heat figures above still apply. Our ASA vs PETG guide covers the UV side in more depth.

Annealing: only where the maker documents it

Annealing means heating a finished print for a set time. Some makers publish annealing settings and some say not to. Here's what the data sheets on this page say:

Of these, only Polymaker HT-PLA and Prusament PC Blend Carbon Fiber publish heat figures both before and after annealing. Bambu Lab's annealed sheets (PLA Basic, ABS, ASA, PC, PAHT-CF) give heat figures only from annealed specimens, so they don't show what annealing changes. Its sheets say "The annealing effect depends on the annealing temperature, time and the model itself," and that "some prints may deform and warp after annealing."

Don't use one maker's cycle on another maker's spool, and don't expect annealing to rescue standard PLA if the maker publishes no setting for it.

Which material should you use for the next print?

Work from where the part will live, then check the exact spool's data sheet.

• Indoors, at room temperature: PLA is fine. Prusa calls it suited to models that "don't require high mechanical, chemical, or temperature resistance." Polymaker HT-PLA is a PLA its maker sells for heat; check its figures above against your need. Our PLA printing problems guide covers PLA's other common problems.
• Warm, but not hot, and on an open-frame printer: PETG. Each maker's PETG sits above its PLA in the tables above. See PLA vs PETG.
• Hotter, or in strong sun for years: ASA. Each maker's ASA sits above its PETG in the tables above, and makers back its UV resistance. See ASA vs PETG and ABS vs ASA.
• Hotter, indoors or out of the sun: ABS. See PETG vs ABS and PLA vs ABS.
• Higher still: PC and carbon-fiber nylon have the highest figures in each maker's table. Check the nozzle, enclosure and annealing needs on the data sheet first.

ABS, ASA and PC come with printing demands PLA and PETG don't. Bambu Lab's filament guide says ABS, ASA, PC and PA "Require higher heatbed and chamber temperatures to suppress warping and layer separation." The comparison guides above cover enclosures and ventilation for each.

A sensible order

1. Note what the part is made of, and the highest temperature it will see if you know it.
2. Find the data sheet for that exact spool. Note the HDT, the load it was tested at and how the specimens were treated.
3. Compare candidate materials from the same maker at the same load.
4. Allow a margin for thin walls, low infill or a part carrying weight.
5. Anneal only if the maker of that spool publishes a setting, and follow it.
6. Reprint in the material that fits, with the printer setup its maker asks for.

Checklist

• The part deformed after printing, not on the bed.
• Material and exact product identified.
• Data sheet found, with HDT, load and specimen notes.
• Comparison made at the same load, within one maker.
• PLA ruled out for warm places, per Bambu Lab's 50 ℃ and Prusa's 60 °C statements.
• Thin or loaded parts given extra margin, or redesigned thicker.
• Annealing only on a maker-documented cycle, in a suitable oven.
• UV needs checked separately from heat for parts in the sun.

How this guide was checked

This is a research-based guide. We haven't heat-tested prints for it. Every heat figure, test standard, load and annealing setting comes from the Bambu Lab, Polymaker and Prusa documents listed in the sources, retrieved on 2026-10-12 (the Prusament PLA data sheet on 2026-10-14). Data sheet versions are given where the document shows one. Where a maker's pages disagree with each other, we've said so and pointed to the data sheet. Read more in our editorial standards.

Print problems: what to check before you buy ↗