Filaments are not interchangeable. A part that's perfect on a shelf will sag into a curve on a dashboard, and it's entirely predictable which one will do it.
Indoors, decorative
PLA. Prints beautifully, takes fine detail, comes in every colour going. It softens around 55°C, which is comfortably below the inside of a parked car in July.
Functional, some weather
PETG. Tougher, slightly flexible instead of brittle, and it copes with heat and damp. This is the default for brackets, outdoor signage and anything that gets handled.
Permanently outside
ASA. UV stable, so it doesn't chalk and go brittle after a summer. It's the right answer for exterior signage letters and anything mounted on a building.
Needs to squash
TPU. Rubbery and grippy — gaskets, feet, protective sleeves. Slower to print, worth it when nothing rigid will do.
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