PLA and PETG
If you only ever learned two filaments, these would be the two. Between them, PLA and PETG cover the large majority of printed parts, and they split the world neatly: PLA is the one that prints beautifully and holds a shape, PETG is the one that survives being used. Knowing exactly where each stops saving you and starts failing you is most of what you need to choose well.
PLA: precise, stiff, and easy — until it gets warm or hit
PLA is the default for a reason. It melts at a low temperature, barely warps, and lays down crisp, accurate beads, so it resolves fine detail and holds dimensions closer to what you drew than anything else. It's stiff, which makes it feel solid, and it's cheap. For prototypes, jigs, brackets, display models and anything that lives indoors on a shelf, it's the right answer and the easy answer at once.
Its two weaknesses are specific and worth memorising. First, heat: PLA starts to soften around 55 °C. That's below the inside of a car on a summer day, below a sunny windowsill, below a part clamped near a motor or a power supply. A PLA bracket that's perfect on your desk can slump into a droop where it's actually used. Second, impact: PLA is stiff but brittle. It doesn't bend and absorb a blow — it cracks. A part that gets dropped, snapped onto something repeatedly, or loaded suddenly is living dangerously in PLA.
PETG: tougher and heat-happy, at the cost of a fussier print
PETG is what you reach for when PLA's two weaknesses are the whole problem. It shrugs off more heat (softening closer to 70 °C), takes an impact by flexing a little instead of shattering, and stands up to water, humidity and many chemicals — which is why it's the plastic of choice for things that get wet, live outdoors briefly, or need to bend slightly without breaking. It also bonds well between layers, so PETG parts tend to be less brittle along the Z axis than PLA.
You pay for that in printability. PETG is stringy — it oozes fine hairs between features that PLA wouldn't (the fix is in Stringing and blobs) — and it's sticky in a way that cuts both ways: it welds to itself well, but it can fuse too hard to a smooth bed and tear the plate, or bond to support so tightly the support won't come off. It likes to print slower and hotter than PLA, and it's less forgiving of a badly tuned first layer. None of this is hard once you've calibrated it; it's just not the point-and-shoot experience PLA is.
| PLA | PETG | |
|---|---|---|
| Prints easily | Yes — the easiest | Moderate — stringy, sticky |
| Detail & accuracy | Excellent | Good |
| Stiffness | High | Medium (slightly flexible) |
| Impact / toughness | Brittle — cracks | Tough — flexes |
| Heat before it softens | ~55 °C | ~70 °C |
| Water / chemicals / UV | Poor | Good |
| Best for | Prototypes, fixtures, display | Functional, wet, mildly warm parts |
What this means in the model
The choice isn't only about the finished part — it changes what you can draw. PLA's stiffness and brittleness mean thin, springy features fail fast: a snap-fit cantilever that flexes on every use will eventually crack in PLA, where the same geometry in PETG flexes and lives. If you're designing a clip, a hinge or anything that bends in service, PETG (or a flexible material) buys you a fatigue life PLA can't. The reverse is also true: for a rigid jig that must not deflect and never flexes, PLA's stiffness is a feature.
And remember the two behave differently on your dimensions. PETG shrinks and spreads a touch more than PLA, so a clearance dialled in for PLA usually needs opening up a little in PETG. Don't inherit a fit blindly across the two — confirm it, the way Real printed clearances and a quick test coupon teach.
When "warm" turns into "genuinely hot," or "used hard" turns into "abused," you've outgrown this pair. That's what ABS, ASA and higher-temp plastics are for.