ABS is three monomers doing three jobs. Acrylonitrile brings chemical resistance and hardness. Butadiene forms a soft rubbery phase dispersed through the mix, and that phase is what absorbs an impact instead of cracking. Styrene supplies rigidity, gloss and the flow that lets the whole thing be moulded cheaply. It has been the plastic of small appliances, keyboard keycaps and interlocking toy bricks for sixty years, and it arrived on desktop printers because it was already the cheapest tough thermoplastic in the world.
Every difficulty ABS causes on a printer comes from one of those three components, which makes it an unusually explainable material.
Warping is a temperature gradient, not a shrinkage number
ABS contracts between 0.4% and 0.8% as it cools, roughly double PLA. That number alone is not the problem. The problem is that ABS stays rubbery until it drops past a glass transition around 105 °C, and in a cold room a fresh layer crosses that threshold within seconds while the layers beneath it are already rigid. The new layer tries to contract and the old one refuses. Stress accumulates layer by layer until something gives: the corner peels off the plate, or the part splits horizontally halfway up.
That is why the fix is chamber temperature rather than bed temperature. An enclosure holding ambient at 50 to 60 °C does not stop ABS shrinking — it shrinks the same amount in the end — but it lets each layer cool slowly and evenly, so the stress relaxes instead of building. Bed at 90 to 110 °C, nozzle 230 to 260 °C, part cooling fan essentially off. Anyone arriving from PLA has to unlearn the fan.
For dimensions, work the shrinkage backwards. A 200 mm enclosure panel comes out at 199.2 mm at the bottom of ABS's range and 198.4 mm at the top — a correction of 0.80 mm or 1.61 mm depending on which end of the spread your spool and chamber land on. Two panels that have to meet along that edge will not, and no amount of slicer fiddling substitutes for measuring a test coupon in your own machine. Both figures come from the shrinkage compensation calculator.
The butadiene phase is why ABS dies outdoors
Butadiene is a diene: its backbone carries carbon–carbon double bonds, and double bonds are exactly what ultraviolet light and atmospheric oxygen attack. Sunlight breaks them, the rubbery phase oxidises and hardens, and the part yellows, chalks and then cracks along the surface it used to bounce off. Months, not years.
This is not a coating problem or a pigment problem, and it is the single reason ASA exists: swap the butadiene rubber for an acrylic ester rubber with a saturated backbone and the same material becomes weatherproof. If a part is going outside, that swap is the whole decision.
The smell is styrene, and it is worth taking seriously without panic
Hot ABS releases styrene along with ultrafine particles small enough to reach deep into the lungs. Styrene is a recognised irritant with a sweet, solvent-like odour that most people notice at concentrations well below anything harmful — which is genuinely useful, because your nose is an early warning rather than a symptom.
The practical position: an enclosure that vents outdoors or filters through activated carbon, and not printing ABS overnight in a bedroom. That is proportionate. Treating a printed keycap as hazardous waste is not, and neither is printing a large ABS enclosure on an open machine on a desk you sleep next to.
Acetone does something no other common filament allows
Acetone dissolves the styrene–acrylonitrile matrix. Suspend a part above a shallow acetone bath in a sealed container and the vapour softens the outer few tenths of a millimetre, surface tension pulls it smooth, and layer lines disappear into a glossy injection-moulded look. It also seals the part, which is the reason people smooth ABS enclosures that need to keep water out rather than because they care how it looks.
Two honest caveats. Fine detail rounds off and small text fills in, so the technique suits shells and housings rather than models. And the surface stays soft for a day or more while residual solvent leaves — handle it early and you will fingerprint it permanently.
What ABS is genuinely bad at
- Tensile strength. This is the surprise. ABS pulls apart between 30 and 45 MPa, below PLA and below PETG. People reach for it believing it is the strong option; what it actually offers is impact toughness and heat resistance, which are different properties entirely.
- Anything outdoors, for the butadiene reason above.
- Open-frame printers, at any part size that matters. Small parts sometimes survive; a large flat base never does.
- Damp filament. Wet ABS prints hazy and rough and cracks along layers. Four to six hours at 65 °C fixes it.
- Bare plates. It wants a hot bed plus a release-and-grip layer — a glue-stick film on smooth PEI is the reliable combination, and an ABS-in-acetone slurry is the traditional one.
What people actually make from it, and one thing they should not
Electronics enclosures, automotive interior clips and brackets that sit in a car in summer, tool housings, and anything destined for the acetone jar. Its heat deflection between 88 and 100 °C is the real reason to accept the printing difficulty.
The thing people wrongly print in ABS is a first functional part on a new open-frame printer, chosen because a forum said ABS is stronger. It is not stronger in the sense they mean, it will warp off the plate, and PETG would have done the job on the first attempt. The comparison against PETG sets out where that flips.
Cost and where it sits
ABS is among the cheaper filaments, typically $18 to $30 per kilogram, and its low density — 1.02 to 1.08 g/cm³, lighter than PLA and much lighter than PETG — means a kilogram goes further than the price alone suggests. Put 1.04 rather than PLA's 1.24 in your slicer's filament profile before you read a grams figure off it — the length and weight converter shows what that difference does to a spool — and then the grams you paste into the print cost calculator describe the part you are actually printing. Leave the PLA figure in place and every ABS quote you produce is wrong in the same direction.