Ten years ago the functional-parts answer was ABS, because the alternative was PLA and PLA melts in a car. PETG arrived in the middle of that gap and took most of the work, not because it is better at anything ABS is famously good at, but because it is good enough at those things while being enormously easier to finish a print in.
The verdict: use PETG unless the part will run above 80 °C, needs a vapour-smoothed surface, or is being printed with dissolvable support in a dual-material machine. Those three cases are still ABS. Everything else has moved.
The ceiling that decides it
PETG holds shape to 68–80 °C; ABS to 88–100 °C. That twenty-degree band is the whole of ABS's thermal advantage, and it matters far less often than it is invoked.
The temperatures a hobby part actually sees cluster in two places. Room and outdoor conditions, including a sun-baked dark surface, sit under the PETG figure with margin. Engine bays, enclosure interiors near a heated bed, and anything bolted to a machine that gets hot sit above the ABS figure too, and want polycarbonate or a filled nylon rather than either of these. The band between the two is real but narrow: a parcel shelf, a window fitting in a hot climate, a light fixture near a filament bulb.
So ask what the part's worst hour looks like. If you cannot name a moment where it passes 80 °C, ABS's headline advantage is not being spent.
The same job, priced twice
Failure rate is the term this comparison actually turns on, and it is invisible on a spool label. Here is a 180 g enclosure panel that takes 7.5 hours on an enclosed machine at 110 W, with filament bought at $22/kg. Machine time is priced throughout at 50 cents an hour, and the power at the United States residential average — the exact figure is in the deep link below, so you can swap your own market in.
At a 6% failure rate — a settled material on a machine you trust — it costs $8.36 per good part: $3.96 of filament, 14 cents of electricity, $3.75 of machine time and a 50-cent failure allowance.
Change one input. At a 30% failure rate, which a large flat ABS part will hit on a marginal enclosure or in a draughty room, the same job costs $11.22. Nothing else moved: same grams, same hours, same watts. The whole difference is the surcharge for attempts that ended in the bin. Every field except the failure rate stayed where it was, which is why that one is where optimism costs real money. The cost calculator is loaded at the pessimistic end, so you can walk it back down to whatever your enclosure actually delivers.
That is the honest economic case for PETG, and it is nothing to do with the price per kilogram — the two materials overlap almost exactly at $18–30 for ABS and $18–30 for PETG.
The three jobs PETG cannot take
Acetone smoothing. ABS dissolves in acetone vapour; PETG does not dissolve in anything you want in your house. If the part needs a glossy sealed surface over compound curves, this is not a preference, it is the only process available on a desktop.
Continuous service above 80 °C. The material spends its heat resistance the moment it is loaded, so a part that is warm and stressed fails well below its published deflection figure. If it is both hot and loaded, ABS buys you real margin that PETG cannot.
Dissolvable support in a dual-material print. ABS pairs with HIPS, which limonene removes without touching the ABS. PETG's soluble partner is BVOH, which is dearer and shorter-lived on the shelf — see PVA against BVOH for why that choice is not symmetric.
Where PETG is genuinely the more annoying material
It is not all one direction, and pretending otherwise is how people end up disappointed.
- Overhangs droop. PETG sags on unsupported spans in a way ABS does not, so models with bridges want either support or a slower, cooler bridging profile.
- It strings until retraction is dialled in. ABS is comparatively clean straight out of a stock profile.
- It does not glue. Cyanoacrylate and most solvent cements barely wet it. ABS can be welded to itself with acetone, which for multi-part assemblies is a large practical advantage.
- It has to be dry. ABS is happier being left out than PETG is.
The plate problem, in both directions
These two materials fail at the build plate for opposite reasons, which is worth knowing because the fixes are opposites too.
ABS does not want to stay down: it needs a hot bed and usually an adhesive film to hold the first layer against contraction. PETG does not want to let go: it bonds to smooth PEI hard enough that people damage plates removing parts, so the same glue stick that helps ABS stick is used with PETG as a deliberate release layer. If a part is stuck fast, that has its own diagnosis.
Picking, in one question
Name the hottest hour the part will see. Under 80 °C and not being polished: PETG, and you will spend less time watching it print. Above it, or headed for an acetone jar: ABS, and budget for the enclosure, the ventilation and the failure rate that comes with it.