The best filament for outdoor use: ASA, PETG or something else?
For parts permanently exposed to the sun, ASA is the safest choice. PETG works in shade or around water; PLA is for short-term or sheltered use.
The short answer
- ASA: direct sun and years of exposure.
- PETG: partial shade, rain and damp; limited UV resistance.
- PC and PA12 with a UV stabiliser: mechanically stressed parts, but harder to print.
- PLA: short-term or indoor use only.
Quick comparison
| Material | UV and sun | Heat | Water and damp | Printing |
|---|---|---|---|---|
| PLA | Poor | Lowest: softens first | Poor over time (hydrolysis) | Easy |
| PETG | Limited | Medium: dark parts in full sun may soften | Good | Medium |
| ASA | Good | Good | Good | Harder: enclosure recommended |
| PC (UV-stabilised) | Medium to good, between PETG and ASA | High | Good | Hard |
| PA (nylon, UV-stabilised) | Depends on type | — | Absorbs moisture; PA12 less than PA6 | Hard |
What the sources say
- Transparent or light PETG can yellow within 3–6 months of intense sun and turn cloudy after 6–18 months; dark colours delay this [1].
- Pure PLA can darken within weeks and become brittle within months, due to UV and hydrolysis [1].
- PC without a UV stabiliser yellows after roughly 2–4 months of intense sun; stabilised grades last about 12–18 months in intense UV or 4–5 years in moderate exposure [1].
- ASA is designed for outdoor use: the guide cites exterior car parts expected to last 5–10 years [1].
These are guide values from manufacturer data sheets and tests: they depend on the product, colour, part orientation and climate.
How to choose the spool
- Look for “UV-stabilised” and references to standards such as ASTM G154 or ISO 4892: the material name alone is no longer enough [1].
- Colour matters: a black part in the sun gets far hotter than a light one, and dark PETG can soften [1].
- Light or transparent PETG is the least suitable for direct sun.
How to print ASA
From the Prusa material guide: nozzle 220–275 °C, bed 90–110 °C, enclosure recommended and glue stick on the plate [2]. ASA emits styrene: ventilate the room well and read Filaments and health.
How to make the part last longer
- Primer plus a UV-protective clear coat: check it every 1–2 years [1].
- Thicker walls (more perimeters): the part tolerates loads and surface wear better.
- Orient the part so the load does not split the layers (see layer adhesion).
- Keep away from heat sources: a PLA or PETG part left in a car in the sun can deform.
Quick examples
- Sensor holder in the shade, planter, sheltered garden hook: PETG.
- Bracket in the sun, exterior car part, sprinkler mount: ASA.
- Seasonal decoration or prototype: PLA is fine, knowing it will not last.
Sources last checked: November 2026. Values are indicative: always check your spool manufacturer’s data sheet.