Choosing a filament
The material is the other half of the machine. You can dial in a perfect model and a perfect slicer profile, and still get a part that snaps in your hand or sags in the sun — because the filament you loaded was the wrong one for the job. Material decides more about how a printed part behaves than any single setting: how strong it is, how it takes heat, whether it survives outdoors, how much it shrinks away from the numbers you drew. This article is the map for the section: pick the family by the property that actually matters for your part, then read the article that goes deep on it.
Start from the property that would make the part fail
Don't start from "what's popular." Start from the one thing that, if you get it wrong, ruins the part. A desk organiser fails if it's a pain to print; a phone mount left on a dashboard fails if it can't take heat; a strap fails if it can't flex; a gear fails if it wears out. Each of those points at a different family, and once you know which failure you're designing against, the choice mostly makes itself.
- Just needs to print clean and hold its shape — prototypes, fixtures, brackets, display pieces: PLA. Stiff, precise, the easiest thing to print, and cheap. Its weakness is heat and impact.
- Has to take some abuse, moisture or mild heat — enclosures, functional parts, anything that lives near water or in a warm-ish spot: PETG. Tougher than PLA and far more forgiving of heat and chemicals, at the cost of a stringier, fussier print.
- Has to survive real heat, sun or hard use — car interiors, outdoor mounts, tools: ABS/ASA (ASA when the sun hits it). Strong and heat-resistant, but they warp and want an enclosure.
- Has to bend and spring back — straps, gaskets, grips, feet, living hinges: TPU. A rubber you print, chosen by hardness rather than stiffness.
- Has to be stiff, dimensionally rock-solid or wear-resistant — jigs, structural parts, gears: filled and engineering plastics (carbon/glass-filled, nylon, PC).
| Family | Ease of print | Stiffness | Toughness | Heat (HDT — the temperature at which the material softens under load) | Outdoor / UV | Reach for it when… |
|---|---|---|---|---|---|---|
| PLA | Easiest | High | Low (brittle) | ~55 °C | Poor | It just has to print well and look right |
| PETG | Moderate | Medium | Good | ~70 °C | OK | It sees water, chemicals or mild heat |
| ABS / ASA | Hard | Medium | Good | ~95 °C | ASA: good | It sees real heat or the sun |
| TPU | Moderate–hard | Low (flexes) | Very high | Varies | Good | It has to bend and return |
| Filled / PC / nylon | Hard | Very high | Varies | High | Varies | It has to be stiff, stable or wear-hard |
Whatever you pick changes your numbers
There's a catch that trips up every designer who switches material without thinking: the material moves your dimensions. Every filament shrinks by a different amount as it cools, flows a little wider or narrower, and wants its own temperature. A clearance you calibrated in PLA — the gap that made two parts click together — can seize or rattle in PETG or ABS, because those shrink more and shift the real size of the printed feature. A press-fit tuned for one filament is a guess in another until you reprint the test.
So treat material choice as a decision that reaches back into the model. When you commit to a family, you commit to re-checking the fits that matter with a test coupon — the physics of why the printed size drifts from the drawn size is in Real printed clearances, and the habit that keeps you honest is in Validate before you print. Change the filament and your saved numbers are provisional again.
The two you'll reach for most often are PLA and PETG — the everyday pair that covers the large majority of printed parts. Start there: PLA and PETG.