PETG or PLA: Which Material Fits Your Part?
PETG and PLA behave very differently under heat, load and outdoor exposure. A practical comparison with the decision rules we use in production.
PLA and PETG are the two materials most parts start with. They print on the same machines, cost roughly the same, and look similar on a datasheet. In service they behave very differently.
The usual question is which one is stronger. That is the wrong question. The better question is which failure mode your part will see first: heat, impact, sustained load, or UV.
What is stiffer, what is tougher
PLA has the higher tensile strength and the higher stiffness of the two. A PLA bracket deflects less under a static load than the same bracket in PETG. That is why PLA test bars usually look better on paper.
PLA is also brittle. It fails suddenly, without warning, and it fails along layer lines. PETG is tougher: it bends, absorbs impact and usually deforms before it breaks. For a part that gets dropped, clamped, or handled on a shop floor, that difference matters more than the tensile number.
Heat is the deciding factor in most cases
PLA softens at roughly 55 to 60 degrees Celsius. That is below the temperature inside a parked car in summer, below the surface temperature of a dark part in direct sun, and below the air temperature next to many motors and power supplies.
PETG stays usable to roughly 70 to 75 degrees Celsius. That is not a high temperature material either, but the extra 15 degrees cover a large share of real indoor and light industrial applications.
If the part will see more than 75 degrees, neither material is the answer. That is where ABS, ASA, PC or PA belong.
Outdoor use and UV
PLA outdoors is a short term solution. It absorbs moisture, becomes brittle under UV and creeps under load in warm weather. PETG holds up better against moisture and everyday weather, but it is still not a UV stable material over years.
For permanent outdoor parts, ASA is the correct choice. It was developed for exactly this case and keeps its colour and impact strength far longer than PETG.
Creep: the failure nobody plans for
Both materials creep, which means they slowly deform under a constant load even well below their yield strength. PLA creeps more, and it creeps faster as temperature rises. A PLA clamp that holds fine on day one can be visibly deformed after two weeks under the same load.
If your part carries a permanent load, treat PLA as unsuitable and PETG as the minimum. For anything structural and permanent, go to PA12, PA6-CF or PC.
Printing and dimensional accuracy
PLA is the easier material to print. It has almost no warp, holds tight tolerances and gives clean surface detail. PETG shrinks slightly more, is more sensitive to moisture in the filament, and tends to string if the material is not dried properly.
In production that difference is manageable. We dry PETG before every run and adjust retraction per spool. For a part with press fits or fine threads, expect PLA to hit the nominal dimension slightly more reliably.
Layer adhesion and watertight parts
PETG has notably better layer adhesion than PLA. A PETG part is closer to isotropic, which means it is less likely to split along a layer line when loaded in the Z direction. It is also the better choice for parts that need to hold liquid, since the layers fuse more completely.
The decision rules we use
- Visual model, fit check, jig used once: PLA. It is cheap, fast and dimensionally accurate.
- Functional part used indoors below 60 degrees, handled by people: PETG.
- Part that gets dropped, clipped, or takes impact: PETG.
- Part in a car, near electronics, or in direct summer sun: not PLA. PETG at minimum, ABS or ASA if it is permanent.
- Part exposed to weather for more than a season: ASA.
- Part under permanent mechanical load: PA12, PA6-CF or PC, not PLA or PETG.
- Part in contact with water or mild chemicals: PETG.
In our own production, most functional orders end in PETG and most visual or first iteration orders end in PLA. Parts that fail in the field almost always failed because PLA was used where heat or creep was involved.
If you are unsure, send us the part with a short note about the load, the temperature and the environment. We will tell you which of the two is enough, and when it is worth moving up a class.