ASA was developed for car wing mirrors, caravan panels and garden furniture — parts that live in sunlight for a decade and must not go chalky. It reached filament spools much later than ABS did, and it arrived to solve one problem that ABS genuinely cannot.
Structurally the two are near-twins. Both are a rigid styrene–acrylonitrile matrix with a soft rubber phase dispersed through it, and that rubber phase is the only meaningful difference. ABS uses polybutadiene, whose backbone is studded with double bonds. ASA uses an acrylic ester rubber whose backbone is saturated — no double bonds for ultraviolet light and oxygen to break. Everything else about the material follows the styrenic script.
What that swap actually buys
Outdoor life measured in years rather than months. An ABS part exposed to direct sun yellows, loses its surface gloss and turns brittle over a single summer. The equivalent ASA part holds its colour and its impact strength through repeated seasons, which is why it is the standard choice for exterior automotive trim rather than a hobbyist preference.
The rest of the property sheet barely moves. Heat deflection between 90 and 105 °C, tensile strength 35 to 50 MPa, the same acetone response, the same rigid feel in the hand. If someone tells you ASA is stronger than ABS, the honest version is "marginally, and not for a reason you will notice".
It warps exactly as badly, and pretending otherwise loses prints
Shrinkage sits between 0.4% and 0.8%, identical to ABS, and the failure mechanism is identical too. Nozzle 240 to 265 °C — a little above ABS — bed 95 to 110 °C, enclosure mandatory rather than helpful, part cooling off except for the smallest bridges.
If anything ASA punishes a cold draught more than ABS does, because its slightly higher processing temperature means a bigger drop to ambient. Printing it on an open frame next to a window is how people conclude that "ASA is impossible". It is not impossible; it is being asked to do something no styrenic can do.
One tuning note that is specific to ASA rather than inherited: it tends to ooze and string more readily at the top of its window, and the usual reflex — dropping the temperature — costs layer adhesion in a material whose whole appeal is durability. Tune retraction and travel speed first, and drop temperature last.
The mistake that costs real money
ASA is priced above ABS for the same mechanical performance: typically $22 to $38 per kilogram against ABS's $18 to $30. The entire premium is the weathering package. Spend it on a part that lives on a shelf, inside a case or under a desk, and you have bought nothing at all.
There is a second version of the same mistake worth naming. ASA's ultraviolet stability belongs to the polymer, not to the colour. A cheap pigment fades on schedule regardless of how well the plastic underneath it survives, so an outdoor sign in a bargain ASA can go pale while remaining structurally perfect. If colour retention matters, that is a question about the brand's pigment, not about the material class.
Where it goes, and what it costs to get there
Here is a garden fitting costed properly, with the failure rate set at 10% rather than the figure you would use for PLA — warping-prone enclosed prints genuinely do fail, and pretending otherwise is where quoting goes wrong.
| Input | Value | Term | Cost |
|---|---|---|---|
| Filament used | 90 g at $30/kg | Filament | $2.70 |
| Print time | 3.5 hours | Machine time at $0.35/h | $1.23 |
| Enclosure draw | 130 W | Electricity, 0.455 kWh at $0.175/kWh | $0.08 |
| Failure rate | 10% | Failure allowance | $0.44 |
| Total | $4.45 |
The failure allowance is the term worth staring at. It is larger than the electricity by a factor of five, and it is the term most people leave out of a quote entirely. Take that allowance out and the total falls to just over four dollars, which is what an ASA quote looks like when it quietly assumes nothing ever lifts off the plate. The print cost calculator keeps the field on screen for that reason.
A kilogram of 1.75 mm ASA, at its published 1.07 g/cm³, comes to 388.55 m of filament — noticeably more than the same mass of PETG, because the styrenics are the light end of the common filaments. That partly offsets the higher price per kilogram, and the length and weight converter will show you by how much for your own reel.
What ASA is genuinely bad at
- Open-frame machines. Not "harder"; effectively out of reach for anything with a footprint.
- Cost-sensitive indoor work, where the premium is pure waste.
- Fume-free rooms. It is a styrenic and it smells like one. Vent or filter the enclosure.
- Bridging and overhangs with the fan off. You are printing with almost no part cooling, so unsupported geometry sags. Design supports in rather than tuning your way out.
- Fine surface detail, which the low cooling and high temperature both work against.
Real uses, and one common misuse
Antenna and sensor mounts, roof and gutter fittings, exterior enclosures, planter hardware, mirror and light housings on RC and full-size vehicles, and replacement parts for anything already made of ASA — which is a surprising amount of exterior car trim.
The common misuse is printing an outdoor part in ASA and then bonding it with an adhesive that fails in UV, or mounting it with printed PLA hardware. The weakest part of an outdoor assembly sets its life, and it is rarely the ASA. Where the choice is genuinely between ASA and a copolyester, the ASA and PETG comparison is the one to read.