ABS vs ASA: Heat, UV, Warping, and Ventilation

Who this comparison is for

This guide is for someone who has outgrown PLA for a particular job: a bracket that lives in a car, a mount on a garden fence, a printer part near a heated bed, or a housing that sits in the sun. ABS and ASA are the usual next step, and they look very similar on a spec sheet. The differences that matter are how each copes with sunlight, how much each fights you while printing, and what you need around the printer to do it responsibly.

Everything below compares the materials in general terms, using manufacturer documentation from Prusa Research, Polymaker, and Bambu Lab, plus emissions research from UL Research Institutes. Individual products vary. Always read the data sheet and recommended settings for the exact spool you plan to buy.

What is the difference between ABS and ASA?

ABS (acrylonitrile butadiene styrene) and ASA (acrylonitrile styrene acrylate) are close relatives. Polymaker's ASA page puts it simply: the two are nearly identical, and "the major difference is ASA is extremely good at weather resistance." Polymaker adds a minor difference, that ASA prints with a matte finish that slightly hides layer lines. That finish note comes from one maker about its own product, so don't assume every ASA looks the same.

Prusa's material guides frame them by use. Prusa describes ABS as a technical material for mechanically stressed parts, listing "good high-temperature resistance" among its strengths, and describes ASA as "a technical material suitable for outdoor use," with temperature resistance up to 93 °C on its ASA guide. Prusament's ASA page goes further and calls ASA "a true successor to ABS," saying that compared with ABS "it's UV stable, it doesn't suffer from shrinking so badly, and the fumes produced are much less noticeable." Treat that as Prusa's description of its own material rather than a guarantee for every ASA on the market. To see Prusament ASA and Polymaker ASA side by side, read Prusament ASA vs Polymaker ASA.

Is ASA better than ABS for outdoor use?

This is the clearest reason to pick one over the other.

• ABS: Prusa's ABS guide lists "Lacks UV resistance (unlike ASA)" as a disadvantage. Its introduction says that compared with ASA there is "slightly worse UV resistance" and that "ABS parts used outdoor turn yellowish and more brittle over time."
• ASA: Prusa's ASA guide lists "High UV resistance" as an advantage. Prusament's product page says its ASA is "UV stable" and that it "will not turn yellow." Polymaker says its ASA is "extremely good at weather resistance" and publishes natural and accelerated aging results for its own material on its product page.

The only lifespan figure among these sources comes from Polymaker, about its own ASA: it says "components exposed to outdoor weather elements (sunlight, rain, temperature fluctuations) maintain integrity for a minimum of two years." That is Polymaker's finding for its own material under its own test conditions, not a promise for other brands or for a part on a south-facing wall in your climate. Color, wall thickness, and the stresses on the part all matter. If outdoor life matters for your project, check whether the exact product publishes weathering data, and plan to inspect the part over time.

Printing requirements

Both materials print hotter than PLA or PETG and both need a heated bed. Here's what each manufacturer publishes. These are starting points for specific products and printers, not universal settings.

Before buying either, confirm that your printer's hotend and bed are rated for these temperatures. Check your printer maker's specifications rather than assuming.

Do ABS and ASA need an enclosure?

ABS is the more demanding of the two. Prusa's ABS guide lists "significant warping" as a disadvantage, says the material demands a higher ambient temperature, and states that the printer should be inside an enclosure. Prusa also notes that ABS typically shrinks around 1 to 2% as it cools, which matters for parts that need to fit something.

ASA isn't warp-free either:

• Prusa: the ASA guide calls significant warping "the main disadvantage of this material," says the printer should be inside an enclosure to keep a higher ambient temperature, and lists an enclosure as necessary for large parts, even while describing ASA as warping less than ABS.
• Prusament: the ASA page says warping can be eliminated by printing in an enclosure or by adding a tall skirt around the object.
• Polymaker: lists an enclosure as "Needed" for its ASA.
• Bambu Lab: the filament guide groups ABS and ASA with materials that "require higher heatbed and chamber temperatures to suppress warping and layer separation," recommending an enclosed printer.

Without an enclosure, Prusa suggests PrusaSlicer's draft shield as a partial measure. Prusa also says to keep the room ventilated while avoiding drafts directly on the print, since drafts cause warping. Our enclosure planning guide covers what an enclosure does and doesn't do, and warping troubleshooting walks through the other causes of lifted corners.

Cooling, build surface, and moisture

• Part cooling: Polymaker lists the cooling fan as off for its ASA. Prusament's page lists 30% fan for Prusament ASA. Follow the profile for your exact filament.
• Build surface: Prusa recommends a smooth or powder-coated PEI sheet with glue stick for both ABS and ASA. Bambu Lab lists both as "Not recommended" on its Cool Plate. See textured vs smooth build surfaces and first-layer adhesion if prints won't stay down.
• Drying: Prusa notes that ASA partially absorbs moisture. Polymaker lists drying its ASA at 70 °C for 7 hours, and Bambu Lab lists drying for both ABS and ASA as "Recommended" at 80 °C for 8 hours. Use the figure for your own spool and check that your dryer and spool can tolerate it. Our filament storage guide and dryer vs dry box guide cover the options.

Emissions and ventilation

This section applies to both materials equally, and it's the part most people underestimate.

Prusa's ABS guide warns that ABS "releases fumes and substances that could pose a potential health risk," and its ASA guide says ASA "releases potentially dangerous fumes during printing." Both guides call for a well-ventilated room. Prusa does say ASA doesn't smell as much as ABS, but a weaker smell is not evidence of lower exposure, and Prusa doesn't make that claim.

UL Research Institutes, summarizing a consolidated study of chamber emissions data published in Environment International, names nylon (particles), ASA, ABS, and HIPS as high-emitting filament materials. UL also notes that emissions depend on both the filament material and print conditions. The UL summary doesn't rank ABS against ASA, so we don't either.

UL's Chemical Insights guidance sets the priorities clearly:

• Ventilation comes first. UL's highest priority is to place printers where there is enough ventilation to dilute emissions, or to use dedicated local exhaust ventilation that vents directly outside.
• Filtration comes next. UL says enclosures should be equipped with HEPA filters for particles and activated carbon filters for VOCs.
• Placement matters. UL advises never placing a printer near a return-air vent, because it recirculates emissions through the building.
• Masks aren't the answer. UL says standard dust masks are not effective against ultrafine particles or VOCs.

UL reports that in its research a ventilated enclosure reduced particle concentration by 99.7% and TVOC concentration by 69.5%. Those are UL's research figures for a ventilated setup, not a promise for any enclosure or filter you can buy.

Can you acetone-smooth ABS and ASA?

Both materials respond to acetone:

• Prusa (ABS): the ABS guide lists easy post-processing, including acetone smoothing, as an advantage.
• Prusa (ASA): the ASA guide says ASA "can be dissolved in acetone" for smoothing.
• Prusament: the ASA page says it can be smoothed with acetone vapors and glued with acetone.
• Polymaker: says its ASA can be smoothed with acetone but points to its own PolySmooth system as a safer alternative.

Acetone is a highly flammable solvent: the NIOSH Pocket Guide classes it as a Class IB flammable liquid with a flash point of 0 °F. Prusa's chemical smoothing article tells readers to work in well-ventilated areas away from flammable objects, wear gloves and face or eye protection, keep any heating outside the smoothing box, and not seal the box completely so pressure can't build up. It also says that if you heat acetone, you do so at your own risk. We don't publish step-by-step smoothing instructions. If you try it, follow the manufacturer's procedure, keep ignition sources away, and never use a kitchen appliance or improvised heater.

Side-by-side comparison

All figures are manufacturer-published or research values for specific products or studies. Other brands and grades differ.

Who should choose which

Choose ASA if:

• The part will be outdoors or behind a sunny window.
• Color and surface appearance need to hold up in sunlight.
• You're printing on an enclosed printer and want somewhat less warping than ABS, per Prusa.

Choose ABS if:

• The part stays indoors and needs more heat resistance than PLA or PETG.
• You want a widely available engineering material for printer parts, jigs, or housings. If you're weighing a "plus" grade, see ABS vs ABS+.
• You plan to acetone-smooth and can do it safely, following manufacturer guidance.

Who should skip both

• You don't have an enclosure or a controlled chamber. Every source here expects one for good results.
• You can't ventilate the space. If the printer lives in a bedroom, a shared living space, or a room without a way to exhaust air outdoors, neither material is a good fit. Ventilation is the first control UL recommends.
• The part only needs moderate warmth or weather resistance. PETG may be enough. Bambu Lab's filament guide describes PETG as not prone to warping, with no mandatory chamber temperature, so it can print on open-frame or enclosed printers (Bambu still recommends an enclosed printer for PETG's interlayer strength). Our PLA vs PETG guide summarizes what Prusa and Polymaker publish on PETG's heat and outdoor behavior, so check whether it covers your project before committing to ABS or ASA.
• Your hotend or bed can't reach the temperatures above. Check your printer maker's specifications first.

Quick answers

Is ASA better than ABS for outdoor parts? Prusa's ABS guide says ABS "Lacks UV resistance (unlike ASA)," while its ASA guide lists "High UV resistance" as an advantage. Polymaker says its own ASA maintains integrity outdoors for a minimum of two years, under its own test conditions.

Does ASA warp less than ABS? Prusa says it does, but still calls significant warping "the main disadvantage" of ASA. Prusa and Bambu Lab recommend an enclosure for both materials.

Is ASA safer to print than ABS? Prusa says ASA doesn't smell as much as ABS, but a weaker smell is not evidence of lower exposure. UL Research Institutes names both ABS and ASA as high-emitting materials and doesn't rank one against the other, so plan ventilation for either.

How much heat can ASA take? Prusa's ASA guide and the Prusament ASA page give a temperature resistance of up to 93 °C. Prusa's ABS guide describes "good high-temperature resistance" but gives no figure.

Can you smooth ASA with acetone? Prusa says ASA "can be dissolved in acetone" for smoothing, and Polymaker says its ASA can be acetone-smoothed. Acetone is highly flammable, so follow the manufacturer's procedure and safety guidance.

Before you buy a spool

• Write down the part's environment: sun, outdoor exposure, and the highest temperature it will see.
• Find the exact product's data sheet. Check heat resistance and whether the maker publishes any weathering data.
• Confirm your printer's hotend and bed can reach the recommended temperatures.
• Plan the enclosure, or confirm your printer is enclosed.
• Plan ventilation separately: exhaust to outdoors or HEPA plus activated carbon filtration, and keep the printer away from return-air vents.
• Plan drying and dry storage using the maker's settings.
• If you'll smooth with acetone, read the manufacturer's procedure and safety guidance first.
• Rule out safety-critical, food-contact, child-use, and electrical applications.

Want more on the wider family of engineering materials? The ABS hub, specialty filaments hub, and enclosures hub collect related guides, and the filament finder can help narrow options by use case.

ABS: what to check before you buy a spool ↗