PLA vs PETG: which filament does your print need?

PLA or PETG? Two of the most popular filaments, and on the spool they look almost the same. But they behave very differently. Let's find out which one your next print needs.

Maybe you've been here. You print a phone holder for the car, and after one sunny afternoon, it sags. Or a clip snaps the first time you use it. The print was fine. The plastic was wrong.

So here's this episode's model: a swatch tag. Print one in each material, and feel the difference. Orange is PLA, teal is PETG. A hole to hang it on a ring, and a tongue you can bend. About 4 grams of plastic each.

Three thin windows show how see-through a colour is. They're 0.4, 0.8 and 1.2 millimeters thick. At 0.2 millimeter layers, that's 2, 4 and 6 layers. Hold both tags up to the light: in the same colour, PETG often looks glossier and more see-through than PLA.

Now, pause and guess. Which one is stiffer? A: PLA. B: PETG. Or C: about the same?

It's A, PLA. Surprised? PETG has a reputation for being the stronger one. But stiff and tough are two different things.

Watch the tongues. Push both the same way. PLA bends less: that's stiff. But push further, and it usually snaps clean. PETG bends a lot further first, and often turns white where it's stressed.

Think of a plastic ruler versus a water bottle. PETG is a cousin of bottle plastic: it dents and bends instead of cracking. So for clips and parts that take a knock, pick PETG. For a bracket that must not flex, PLA's stiffness is a plus.

Then there's heat. PLA starts to soften at around 60 degrees Celsius. PETG holds out to about 80. Around that temperature the plastic goes from glassy to rubbery, so a part under load slowly bends. A car parked in the summer sun can get hotter than 60 inside. That explains our sagging phone holder.

PETG buys you about 20 degrees more. But a dashboard in full sun can get hotter still, so for parts right behind the windscreen, look at ASA or ABS.

PETG prints hotter. Start from your slicer's PETG profile, and check the range on the spool. In this example, the nozzle goes from 215 to 240 degrees. That's 25 hotter than the PLA profile.

Then turn the part cooling fan down. Lots of fan gives PLA its crisp details, but with PETG it can weaken the bond between layers. The bed usually runs a bit hotter too. Names differ per slicer.

One warning: PETG is sticky. On a smooth PEI sheet or on glass, it can bond so well that it tears chunks out of the surface. A thin layer of glue stick works as a release layer.

It also sticks to itself. That's why our print-in-place hinge wants a bit more gap in PETG. And it strings more, especially when it's damp. So keep it dry.

So, which one wins? Neither. It's a match, not a ranking. PLA is easy, stiff and crisp: great for models, prototypes and indoor parts. PETG is tough and takes more heat: pick it for clips, parts for the car interior and things that live outside.

In short: PLA is stiff, easy and crisp. PETG is tough and handles more heat. So choose by the job your part has to do, not by the hype.

The swatch tag is free to download. Print it in both, bend the tongues, and tell me in the comments: which part would you only ever print in PETG? I'm Spoolbert, see you in the next one.