PETG and ASA both get pitched as the next material to try once PLA starts feeling too fragile, and buyers’ guides often lump them together as interchangeable upgrades. They are not. PETG is the easier print, tolerant of an open-frame machine, and it shrugs off daily knocks and moisture. ASA is built to sit outside, in direct sun, for years without turning brittle or yellow. The real question is not which one is “better,” it is whether the part’s biggest enemy is sunlight or just ordinary wear.
A different setup before the plastic even matters
PETG and ASA print at similar nozzle temperatures but ask different things of the rest of the printer. Prusa’s Knowledge Base lists Prusament PETG at around 230°C for the first layer and 240°C after that, on a bed near 85°C, with no enclosure required. ASA sits hotter on both counts: manufacturer data sheets and filament comparison sites put its range around 220 to 275°C at the nozzle and 90 to 110°C on the bed, and Prusa recommends printing it inside an enclosure to control warping, the same requirement ABS has and for the same reason. ASA cools unevenly in the open and corners lift before the print finishes; PETG rarely has that problem, a big part of why it became the default step up from PLA for anyone without a heated chamber. ASA also gives off a stronger, more ABS-like smell from styrene, so the same ventilation advice for ABS applies here. PETG is comparatively low odor.
ASA’s outdoor edge, and PETG’s real, not zero, UV resistance
This is the difference that actually separates these materials in practice. Polymaker’s aging documentation reports a color change, Delta E, under 2.5 after two years of natural outdoor aging for its ASA, and under 5 even under accelerated weathering equal to roughly 8,000 kJ/m² of UV exposure, with only minimal loss of tensile strength. Prusa describes ASA in similar terms: UV and weather resistant enough for genuine long-term outdoor use, the main reason it exists as ABS’s replacement. PETG is not UV-proof, but it is not hopeless outdoors either. Manufacturer guidance and independent write-ups call its UV resistance moderate, fine in shade or short-term outdoor use, but direct sun causes visible yellowing, most obvious on clear or light colors, and a gradual loss of toughness, with degradation commonly showing up within one to two years. MatterHackers’ outdoor filament guide notes PETG can lose strength and color after extended sun exposure, while ASA keeps both for years. It is not that ASA survives outside and PETG does not. It is a difference in how many summers the part needs to survive.
Where PETG pulls ahead: layer strength without a chamber
Take UV out of the equation and PETG has an advantage of its own. In side-by-side mechanical testing of Prusa’s matched material lineup, CNC Kitchen found vertically printed PETG parts held onto about 46 percent of the strength of horizontally printed ones, while ASA parts printed the same way, on an open printer, held onto only about 29 percent, snapping at roughly 17 kg against PETG’s 25 kg. Printing the ASA samples in a mildly warmed enclosure, around 30°C, improved that figure by about 20 percent, showing how much ASA’s layer bonding depends on chamber heat most home setups do not provide. ASA hits back on impact resistance: the same testing put it at more than double PETG’s, so a raw ASA part shrugs off a sudden knock better, even with weaker layer bonds. Both materials absorb moisture from the air, but PETG’s sensitivity to it, stringing, weak welds, visible bubbling, is more widely documented and shows up faster.
Which one is actually easier to print
Put the last two sections together and the day-to-day experience tilts toward PETG. It tolerates an open-frame printer, bonds its layers reasonably well without chamber heating, and does not fill a room with smell. ASA behaves like a better-mannered ABS: it wants an enclosure, a warm draft-free environment, and real ventilation. Comparison guides from filament vendors and hobbyist sites consistently rank PETG as the more forgiving, lower-maintenance print of the two, while ASA is treated as the material you graduate to once your setup can support it, the same category ABS has always occupied.
Cost and availability
Price rarely settles this on its own. When CNC Kitchen priced Prusa’s own matched lineup, PETG worked out to about €30 per kilogram against €35 for ASA, though ASA’s lower density meant the two cost roughly the same per meter of filament actually used, about 9 cents. Across the wider market, pricing trackers show PETG with more competing brands and lower entry prices, commonly starting near $8 to $9 per kilogram, while ASA stays a narrower, more specialty category, even as budget ASA options have gotten more competitive over the past year. PETG is easier to find and a bit cheaper on average, but the gap has been closing.
If PETG’s balance against plain ABS is still unclear, the PETG vs ABS comparison covers that pairing directly, and the ABS vs ASA guide looks at ASA’s closest chemical relative. Once you have picked a side, the PETG print settings guide covers dialing it in.
Neither material wins outright, they answer different questions. Choose PETG for parts that need to survive daily handling, occasional chemical exposure, or shaded and short-term outdoor use, and that you would rather print without babysitting an enclosure. Choose ASA for anything that has to sit in direct sun for years, a mailbox, a sign, a drone body panel, where fading and embrittlement are the failure you are actually designing against. The question worth asking before buying either spool is not which one prints easier or costs less. It is how many summers the part actually has to survive outside.