This is the most common material decision in desktop printing, and it has a short answer: PLA for anything decorative, dimensionally fussy or indoors; PETG for anything functional, outdoors or warm. The rest of this page is the reasoning, and the cases where that short answer is wrong.
The measurable differences
| PLA | PETG | |
|---|---|---|
| Density | 1.17–1.26 g/cm³ | 1.23–1.29 g/cm³ |
| Nozzle | 195–225 °C | 230–250 °C |
| Bed | 0–60 °C | 70–85 °C |
| Heat deflection | 52–60 °C | 68–80 °C |
| Tensile strength | 45–65 MPa | 45–55 MPa |
| Shrinkage | 0.2–0.5% | 0.2–0.6% |
| Outdoor / UV | poor | good |
| Enclosure | not needed | helpful, not required |
| Typical price | $15–28 /kg | $18–30 /kg |
Note the tensile row. On paper PLA is the stronger material, and people are frequently surprised by that. Tensile strength measures resistance to being pulled apart before breaking; it says nothing about whether the part shatters or bends when it gets there. PLA is stiff and brittle, PETG is slightly softer and considerably tougher, and for a part that gets dropped or flexed, toughness is the property that matters.
Where the real difference lives: heat
PLA softens between 52 and 60 °C. PETG softens between 68 and 80 °C. A parked car's interior on a summer day comfortably passes the first number and generally stays below the second, which is why "it sagged in the car" is a PLA story and rarely a PETG one.
The underlying property is the glass transition — the temperature at which an amorphous polymer stops behaving like a solid and starts behaving like a very stiff liquid. It is a property of the polymer's chemistry rather than of how the part was printed, which is why no amount of infill, wall count or annealing turns PLA into a material that survives a dashboard. Our sister site PeriodicDeck covers the chemistry side of why different polymer backbones behave so differently at temperature.
Where PLA genuinely wins
Dimensional accuracy and detail. PLA is stiffer in the melt, strings less once tuned, and holds sharp corners better. For a part with a press fit, a thread, or fine text, PLA gives a better result with less tuning.
Overhangs and bridges. PETG droops noticeably more. If the model has unsupported spans and you would rather not add supports, PLA is the easier material.
Speed of setup. No bed adhesive decisions, no drying, a wide temperature window and a forgiving profile. PETG is not difficult, but it is fussier on every one of those.
Where PETG genuinely wins
Outdoors. PLA goes chalky and brittle under ultraviolet within months. PETG holds up for years. This alone decides most garden, roof and vehicle-exterior parts.
Impact and flexing. A PETG clip survives cycles that snap a PLA one. Anything that springs, clips or absorbs a knock should be PETG before it is PLA.
Water and chemicals. PETG shrugs off water contact and most household chemicals. PLA is fine in water short-term but is not a material to build something permanently wet out of.
The practical costs of choosing PETG
Two, and both are avoidable rather than serious.
PETG absorbs moisture noticeably faster than PLA, and wet PETG strings, pops and prints with a hazy surface. This is the single most common PETG complaint and it has a free fix: dry the spool at 65 °C for four to six hours.
PETG also bonds to smooth PEI extremely well — sometimes better than PEI bonds to its own substrate, which is how people take chunks out of a build plate removing a part. Use a textured plate, or a thin glue-stick film as a deliberate release layer, and let the plate cool fully before removing anything.
When the answer flips
Choose PLA for an outdoor part if it will be painted, since paint is a UV barrier and the mechanical requirement may be nil. Choose PETG for a decorative indoor part if it is going somewhere warm, like above a radiator or in a conservatory. And choose neither if the requirement is real heat resistance above 80 °C — that is where ABS, ASA and polycarbonate start, and stretching PETG into their territory is how a part fails in service rather than on the plate.
Cost, honestly
The two materials are close enough in price that cost rarely decides this. Mainstream PLA runs fifteen to twenty-eight dollars a kilogram and mainstream PETG eighteen to thirty, so PETG carries maybe a ten to fifteen percent premium at similar quality.
PETG is also slightly denser — 1.27 against 1.24 g/cm³ — so the same geometry uses about two percent more mass. Between the two effects, an identical part in PETG costs roughly fifteen percent more in plastic. On a forty-gram part that is a difference of pennies, and it should not be what decides the material.
The cost difference that does matter is failures. A PETG print that fails because the spool was damp consumed its filament and its hours and produced nothing, and that is a far larger number than the price premium. Drying is the cheapest insurance available on this comparison.
A short decision rule
Ask one question: will this part ever be warm, wet, outdoors, or flexed? If yes, PETG. If no, PLA, and you will get a cleaner-looking part with less effort.