A car in the sun gets hotter than most filaments can take. The number that decides it is heat deflection temperature.
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How hot a car gets
Researchers at UC San Diego and Arizona State University measured cars parked in the sun on summer days. After an hour the dashboards averaged 157 °F (69 °C) and could pass 165 °F (74 °C), while the air inside reached 116 °F (47 °C), according to the university's report.
A part on the dash or rear shelf sees the top of that range. For cars parked in shade, the same study measured dashboards averaging 118 °F (48 °C), so where the car lives matters as much as where the part sits.
Heat resistance by filament
Heat deflection temperature is where a printed test bar starts to bend under a light load. These are from Prusament's technical data sheets, at 0.45 MPa.
Filament
Heat deflection
UV stable (per Prusa)
Car verdict
PLA
55 °C
Not claimed
Softens well below dashboard temperatures
PETG
68 °C
Not claimed
At the dashboard average, so it can sag in sun
ASA
93 °C
Yes
The usual choice for car parts
PC Blend
113 °C
Not claimed
The most heat resistant, harder to print
Why ASA
ASA clears dashboard temperatures with room to spare, and Prusa describes it as UV stable, so it keeps its toughness and does not turn yellow outdoors. That covers the two things that kill car parts: heat and sunlight.
PC Blend handles even more heat, but it needs a 275 °C nozzle by its data sheet and an enclosed printer. Save it for parts near a heat source.
ASA filament
🖨️400×400 · polymaker-asa.webp
ASA filament
Polymaker ASA filament
UV and weather resistant ASA, 1.75 mm on a 1 kg spool. Polymaker lists 250 °C nozzle and 90 °C bed settings, and an enclosed printer for large parts.
Prusament's data sheet gives 260 °C for the nozzle and 110 °C for the bed. ASA shrinks as it cools, so print it in an enclosed printer and keep drafts away; Prusa's warping guide covers brims and slower speeds for large parts.
Bambu Lab lists ASA as not recommended on the open-frame A1 and ideal on the enclosed P1S. Print it with ventilation, following the filament maker's guidance.
Common questions
It will soften and deform. PLA's heat deflection temperature is 55 °C in Prusament's data sheet, and a dashboard in the sun averages 69 °C.
In a car parked in shade, the study measured dashboards averaging 48 °C, below PETG's 68 °C. On a sunny dash it sits right at the measured average, so ASA is the safer choice there.
Prusa calls ASA a successor to ABS. It is UV stable, shrinks less and gives off less noticeable fumes, so it is the better pick for anything that sees sunlight.
Specifications come from manufacturers' published pages and can change. Check your printer's current documentation before you change a setting or fit a part.