How worried should you actually be about a stray ember or an overheated hotend setting your print — or your print farm — on fire? A blowtorch-and-camera test published August 12 by 3D-printing YouTuber Maker's Muse puts a number of common filament chemistries directly to the flame, and the results split cleanly into two camps: materials that catch fire and keep burning, and materials that simply refuse to.
The test wasn't a marketing exercise or a vague "is PLA flammable" thought experiment, and it comes at a moment when more makers are running unattended overnight prints and multi-printer farms, where an unnoticed ignition source has more time to do damage. Maker's Muse printed samples in ten-plus materials — standard PLA, PLA+, Prusa's Galaxy Black PLA, HTPLA, PETG, ABS, ASA, TPU, PEBA, HIPS, and a foam-structured TPU — and hit each one with a direct blowtorch flame, watching how readily it ignited, how it burned once lit, and whether it kept burning after the torch was pulled away.
The PLA Family Isn't One Material
The most counterintuitive finding involves PLA, a filament most makers treat as a single known quantity. It isn't. Elegoo PLA+ ignited readily under the torch and burned with what Maker's Muse described as a "dirty yellow flame." But other PLA variants behaved very differently: Prusa's Galaxy Black PLA needed sustained blowtorch exposure just to catch — though it then burned hot while melting — and HTPLA (high-temperature PLA, typically annealed and often carrying its own filler package) actively resisted burning, self-extinguishing once the torch was pulled away rather than continuing to burn on its own.
That's a meaningful distinction for anyone assuming "PLA" is a fixed flammability profile. The base polymer is the same, but pigments, fillers, and processing additives appear to change how the material ignites and whether it sustains combustion once lit — which matters far more for real-world fire risk than the polymer name on the spool label.
ABS, ASA, and Foam TPU: The Bad News
On the other end of the spectrum, ABS and ASA — both already known in the printing community for warping, fumes, and the need for enclosures — burned enthusiastically under the torch, producing what Maker's Muse describes as a "sooty yellow flame," the visual signature of incomplete combustion and heavy soot and smoke production. HIPS, another ABS-family material in the test, showed similarly sooty burning behavior. Given that ABS and ASA are already common choices for enclosed, heated-chamber printers running for hours unattended, that combination of flammability and sooty burning is worth sitting with.
The single most flammable material in the entire test, however, wasn't a rigid engineering filament at all — it was foam TPU. The porous, air-filled internal structure that makes foam TPU useful for cushioning and shock-absorbing prints also makes it dramatically easier to ignite than any other material tested, more so even than ABS or ASA. Porous, high-surface-area structures are a classic fire-risk profile in materials science generally — more surface area exposed to oxygen means faster ignition and faster flame spread — and this test suggests the same physics applies squarely to 3D-printed foam parts.
PETG and Solid TPU: The Standouts
At the opposite extreme, two materials stood out for actively resisting fire. Solid (non-foamed) TPU could not be ignited at all in the test, even under direct and sustained blowtorch flame — it simply melted rather than catching, making it the least flammable material in the whole lineup. PETG also proved difficult to ignite, holding up notably better than the readily-igniting PLA+, ABS, or ASA under the same torch exposure.
That's a useful data point for anyone specifying materials for parts near heat sources, electrical enclosures, or automotive/under-hood brackets, where "doesn't easily sustain a flame" is a real design requirement rather than a nice-to-have. It's also a notable result given how differently PETG and TPU are usually marketed — PETG for outdoor durability and chemical resistance, TPU for flexibility and impact absorption — with fire behavior rarely mentioned as a selling point for either. As Hackaday's Maya Posch summarized in her write-up of the test the same day, "PETG and regular TPU seem to be your best bet if you do not want your 3D print to turn into a happily burning candle."
What It Means for Makers
None of this is peer-reviewed flammability testing to a UL or ASTM standard — a blowtorch is a blunt instrument compared to a cone calorimeter, and the test doesn't quantify heat release rate, smoke toxicity, or flame-spread distance. But as a practical, visual comparison of materials makers actually put in printers, it's more informative than most spec sheets, which rarely list flammability behavior at all.
The takeaways are straightforward. First, don't treat "PLA" as a single flammability profile — additives and fillers measurably change how a given spool behaves near heat, and a high-temp or specialty variant may be meaningfully more fire-resistant than the plain stuff on the same shelf. Second, if a print is going to live near a heat source, in an enclosure, or in an application where an ignition source is plausible — a light fixture, an electronics housing, anything sitting on or near a running hotend — PETG or solid TPU are the safer bets of the materials tested here, while ABS and ASA warrant more caution than their popularity might suggest. Third, foam TPU's outlier flammability is worth flagging specifically for anyone using it in wearables, automotive interiors, or padding applications where it might sit near heat: the same porosity that makes it comfortable also makes it burn fast.
None of this means ABS or ASA printers need to be unplugged — enclosed ABS and ASA printing happens safely as a matter of routine, and ignition sources in a well-maintained printer are rare. But "rare" isn't "impossible," and a direct, visual demonstration of which filaments actually sustain a flame versus which ones self-extinguish or simply melt is a useful reference the next time you're choosing a material for a part that will sit near anything hot.
