ASA vs PETG: Which Holds Up Better Outdoors?
If a part is going to live in the sun, print it in ASA. PETG is the easier, tougher-to-print-with material for indoor and shaded work, and it has better chemical resistance, but it yellows, clouds, and gets brittle under sustained UV. ASA was engineered specifically to survive sunlight. That’s the short version, and for most outdoor brackets, housings, and mounts it’s the whole answer.
The longer version matters because “outdoors” isn’t one condition. A part in full New Mexico sun on a south-facing wall lives a very different life than the same part under an eave or inside a vented enclosure. PETG can be fine in the second case for a good while. In the first, it’s on a clock. So the real question is usable versus durable: not which material wins a tensile test, but which one is still doing its job after a few summers. That gap is where people get burned.
The cost of guessing wrong
Material is the cheap part of a printed bracket. The expensive part is the second print run, the trip back up the ladder, and the week the part wasn’t doing its job. Pick PETG for a sun-exposed mount because it printed easily and tested strong on the bench, and you may get a season out of it before it hazes over and a corner snaps off in your hand. Pick ASA for an indoor fixture that never sees UV and you’ve paid more per kilogram and fought warping for protection the part will never use.
Here in Albuquerque the UV math is brutal. High desert, thin atmosphere, intense sun most of the year. The same exposure that fades truck dashboards and chalks patio furniture works on a printed part too. A material that’s “rated for outdoor use” in a mild coastal climate is being asked to do harder work at altitude under a high-desert sun. If your part ships somewhere with that kind of exposure, weight the UV question harder than a generic outdoor guide would tell you to.
How ASA and PETG actually compare
Most of this comes down to two properties (UV stability and heat resistance) plus a printability tradeoff that runs the other way. Here’s the head-to-head, with the caveat every datasheet carries: exact numbers move with brand and grade, so treat these as representative, not gospel.
| Property | ASA | PETG | Edge |
|---|---|---|---|
| UV / weathering | Resists yellowing and embrittlement at the chemistry level | Photodegrades; yellows, clouds, cracks over time | ASA |
Heat-deflection temp (@ 0.45 MPa) | ~87–98 °C | ~68–70 °C | ASA |
| Tensile strength (printed) | ~45 MPa | ~39–42 MPa | ASA, modestly |
| Ductility / layer bonding | Stiffer, less forgiving | More ductile, forgiving layer adhesion | PETG |
| Chemical resistance | Moderate | Better against acids and many solvents | PETG |
| Printability | Needs enclosure, higher temps, ventilation | Prints open-frame, lower temps | PETG |
| Density | 1.07 g/cm³ | 1.27 g/cm³ | PETG denser/heavier |
Why ASA wins on UV: it’s chemistry, not a coating
ASA, or acrylonitrile styrene acrylate, was developed to fix the one place ABS falls apart: sunlight. ABS uses a polybutadiene rubber phase for toughness, and butadiene carries reactive carbon-carbon double bonds that UV light attacks directly, which is why ABS chalks and embrittles outdoors. ASA swaps that rubber for an acrylate one with no such reactive bonds, so it resists UV photo-oxidation in the base polymer itself, not through an additive that wears off. The acrylate UV-resistance story is well covered in the outdoor-filament breakdown the folks at Sovol put together, and it’s the reason ASA is the default for signage, automotive trim, and weatherproof housings. The accelerated-weathering tests behind these claims run to standards like ISO 4892 and ASTM G154 if you want to go down that rabbit hole.
PETG goes the other way under prolonged UV. The polymer undergoes photodegradation (chain scission and oxidation), and the visible result is yellowing, surface clouding, fine cracking, and a loss of toughness over time.
How long does PETG actually last in the sun?
This is the question makers ask most, and the honest answer is: it depends, and nobody can give you a clean lab number. Field reports from people running PETG outdoors cluster around one to two years in constant, intense sun, and longer, several years, in shade or partial sun. A rundown on PETG’s UV behavior from Makershop lands in the same range. Treat that as practitioner experience, not a spec: lifespan swings hard with color (darker and pigmented holds up better than clear or white), wall thickness, how loaded the part is, and how direct the exposure is. If you need a printed part to survive five years of southern-latitude sun without babysitting, that’s an ASA job.
Is ASA stronger than PETG?
Modestly, in tensile: printed ASA runs around ~45 MPa versus PETG’s ~39–42 MPa, and ASA is the stiffer material. But “stronger” is the wrong single axis. PETG is more ductile: it bends and absorbs a hit before it lets go, and its layer-to-layer adhesion is more forgiving, which matters a lot for a functional part that takes load across the print’s weakest plane.
One thing to watch in any spec-sheet shoot-out: impact toughness numbers for these two often aren’t measured the same way (notched versus unnotched test bars), so setting them side by side as if they’re directly comparable will mislead you. The defensible read is qualitative: PETG forgives more, ASA is stiffer and stronger in straight tension. For a part where a clean snap is the failure you’re worried about, PETG’s ductility is a real point in its favor; for one that needs to hold its shape under heat and sun, ASA’s the pick.
Heat resistance
ASA holds its shape to a higher temperature. Heat-deflection temperature, the point where a loaded part starts to sag, sits around 87–98 °C for ASA depending on grade, against roughly 68–70 °C for PETG. That’s the gap between a part that survives a closed car in summer and one that slumps on the dashboard. For anything near an engine bay, a motor, or a sun-baked enclosure, the heat number alone often decides it before UV even enters the conversation.
Does ASA always need an enclosure?
In practice, yes, and this is PETG’s whole case. ASA warps and lifts at the corners on an open frame, wants a hotter nozzle and bed, and gives off stronger styrene fumes that call for ventilation. PETG prints on a bare open printer at lower temperatures, bonds layers forgivingly, and is comparatively low-odor. That’s why PETG is the friendlier material for someone printing it themselves, and a big reason it gets reached for outdoors even when ASA is the better long-term call. If you’re commissioning the part rather than printing it, this tradeoff mostly disappears. We run ASA on enclosed machines because that’s what it takes to get a clean weatherproof part, so the warping and fumes are our problem, not yours.
Should you dry ASA or PETG before printing?
Both behave better dry, but there’s a myth worth correcting here. You’ll see both materials described as “high water absorption,” and for PETG that overstates it. Prusament’s own PETG datasheet measures only about 0.13 % uptake in 24 hours, which is low. Damp filament hurts print quality (stringing, popping, weaker layers), so dry storage is good practice for both. But the idea that PETG soaks up water like nylon and weakens dramatically in service doesn’t hold up against the datasheet. The primary source beats the forum claim on this one.
Chemical resistance and a note on the carbon-fiber versions
PETG has the edge on chemical resistance: it shrugs off many acids and solvents better than ASA, which is part of why it shows up in fluid-handling and splash-exposed parts. If your part contacts chemicals more than it contacts sunlight, that can flip the decision back toward PETG.
Both materials also come in carbon-fiber-reinforced grades (ASA-CF, PETG-CF) that add stiffness and dimensional stability. They don’t change the core outdoor story: ASA-CF still owns UV, PETG-CF is still the easier-printing one, so the decision logic below holds for the filled versions too.
The decision rule
Strip away the spec sheets and it comes down to one question: does the part live in sun and heat, or not?
- Sun, heat, or true weather exposure → ASA. Outdoor housings, brackets, covers, sun-exposed mounts, automotive exterior trim, anything that has to look and work the same after a few summers. ASA’s UV and heat resistance is the engineered answer, and there’s no PETG trick that closes that gap.
- Indoor, shaded, chemical contact, or you just need an easy strong functional part → PETG. Enclosure internals, fluid-handling parts, jigs and fixtures, brackets that never see direct sun. PETG prints easier, bonds layers more forgivingly, and resists chemicals better.
- Edge cases: Shaded-but-warm leans ASA on the heat number. Sun-exposed but chemically attacked is a genuine tradeoff worth a conversation. And if you were weighing ABS too: ABS is tough and heat-tolerant but shares ABS’s UV weakness, so for the outdoor question ASA beats it for the same chemistry reason it beats PETG. (There’s a fuller rundown on each on the ASA, PETG, and ABS material pages.)
One more honest note on cost: ASA tends to run meaningfully more per kilogram than PETG. Practitioners commonly cite somewhere around 40 % more, though prices move and it varies by brand. For a part that would otherwise need replacing every summer, the material premium pays for itself the first time you don’t reprint it.
Want the part printed in the right material?
Choosing between ASA and PETG is the easy half once you know which way the part faces the sun. The harder half is printing ASA well: enclosed, dialed-in temperatures, managed warping and fumes, exactly the stuff a desktop printer in the garage struggles with. That’s the work we do.
We print functional parts in both materials, pick the right one with you if you’re unsure, and stand behind the result. Upload an STL, STEP, or 3MF and get an instant quote. Free delivery across the Albuquerque metro, flat-rate shipping for everyone else. If it’s a weatherproof bracket, a sun-exposed housing, or a replacement for a part the sun already killed, ASA is usually the call, and we’ll print it the way it needs to be printed.