PETG.
THE WORKHORSE.
PETG (glycol-modified polyethylene terephthalate) is the same family of plastic as your water bottle — literally. Add a little glycol modifier to standard PET, and you get a filament that prints almost as easily as PLA, but survives heat, impact, moisture, and chemicals that would destroy it.
If PLA is for looking, PETG is for doing. It's what we reach for when a customer says "it needs to actually work, outside, for a few years." At Spool Foundry this is the default filament for functional brackets, enclosures, fixtures, garage tools, outdoor signage, and most small-run manufacturing jobs.
What it is
PET is the plastic in soda bottles and food packaging — strong, clear, chemically stable, and recyclable. Pure PET crystallizes when you heat and cool it, which makes it a nightmare to 3D print. Adding glycol (the "G" in PETG) disrupts the crystal structure and keeps it amorphous, which is what allows it to flow smoothly through a nozzle and stick to itself in layers.
The result is a filament that combines most of PLA's printability with ABS-class toughness and moisture resistance. It's not quite as easy as PLA and not quite as heat-resistant as ABS, but it gets a lot closer to "best of both worlds" than either extreme.
Technical properties
- EXTRUDER TEMP
- 230 – 250 °C
- BED TEMP
- 70 – 85 °C
- ENCLOSURE
- Optional, helps for large parts
- GLASS TRANSITION
- ~ 80 °C
- HEAT DEFLECTION
- ~ 70 – 75 °C
- TENSILE STRENGTH
- ~ 50 MPa
- ELONGATION
- ~ 4 – 120 % (varies — tough)
- IMPACT RESIST.
- Medium-high — absorbs shock
- UV RESIST.
- Moderate (better than PLA, worse than ASA)
- WATER ABSORB.
- Low, but hygroscopic once opened
- CHEMICAL RESIST.
- Good against acids, bases, many solvents
- FOOD-SAFE GRADES
- Available (but layer porosity matters)
Pros
- Tough, not brittle. Where PLA cracks, PETG bends and absorbs the hit. This is the single biggest reason to pick it. It's not indestructible, but it survives real-world abuse much better.
- Chemical and moisture resistant. Shrugs off water, mild acids, bases, oils, and many solvents. Perfect for garage, garden, and workshop parts.
- Moderately heat resistant. A PETG part will survive a hot car for short periods where PLA would pancake.
- Low warp. Unlike ABS, PETG doesn't curl off the bed dramatically. Prints large parts reliably without an enclosure.
- Good layer adhesion. PETG bonds to itself strongly between layers — the anisotropy (strength difference between print axes) is lower than PLA or ABS.
- Food-safe grades exist. You can buy PETG certified for food contact. But see the warning below about layer porosity.
- Recyclable. Shares a recycling stream with PET bottles in most regions.
- Clear / translucent options. One of the few filaments that can print genuinely see-through parts for light pipes, enclosures, or visibility windows.
Cons
- Stringy if mis-tuned. PETG loves to pull thin strands between travel moves. A well-tuned printer solves this, but dialed-in retraction is essential.
- Sticks too well to some bed surfaces. On smooth PEI or glass it can rip chunks off when you try to remove a part. We use textured PEI sheets.
- Hygroscopic. Absorbs moisture from the air. Wet PETG prints with steam, popping, and layer defects. We dry it before printing batches.
- Not as stiff as PLA. Parts flex more under load. For rigid jigs or fixtures, PLA is stiffer.
- Surface detail is softer. Tiny lettering or micro features look better on PLA.
- Food-safe claim has an asterisk. Even certified-safe PETG has microscopic gaps between layers where bacteria can hide. For a repeatedly-washed food container, injection-molded PET is a better choice.
- Scratches more easily than PLA or ABS. Shows wear on hand-held items.
When to pick PETG
- Functional parts that will be used, not just displayed.
- Outdoor or garage environments — lawn tools, garden hardware, shed brackets.
- Enclosures, cases, and housings for electronics that won't run hot.
- Water-exposed parts — plant pots, aquarium components, plumbing mock-ups.
- Parts that take occasional impact — drop-proof cases, tool handles.
- Anything with moving hinges or flexing features that would crack in PLA.
- Large prints where PLA would warp or ABS would curl.
- Clear or translucent parts — PETG is the best FDM option for see-through.
When not to pick PETG
- Parts that will live inside a car in Florida summer (use ABS or PAHT-CF).
- Parts that need rigid, no-flex stiffness (use PLA).
- Parts with ultra-fine surface detail (use PLA).
- Food containers that will be washed dozens of times (use injection-molded food-grade plastic, not FDM).
- Parts that need to flex like rubber (use TPU).
Design tips for PETG parts
- PETG is more ductile than PLA — it can take slightly thinner walls without cracking. 1.0 mm minimum for non-structural parts is workable.
- Threaded inserts work well in PETG because the plastic gives slightly. Heat-set brass inserts are our go-to.
- Because PETG absorbs moisture, we keep spools in sealed drybags with desiccant and dry them at 65 °C for 4 hours before each long job.
- Design drain channels on outdoor parts. PETG is water-resistant but not waterproof at the layer lines.
- For UV exposure longer than a year, add a coat of UV-resistant spray paint — the base color will still fade without it.
Our take
If you called us tomorrow and said "I need a small part that has to survive two summers in my garage," we would quote PETG without even asking what color. It's the filament we reach for when we don't know what else to reach for, and it's almost never the wrong answer. The one axis where it loses to PLA is looking pretty; every other axis, it wins.
PETG is our house default for anything functional. If you request "whatever you think is best," and the part sounds like it'll actually be used, you're getting PETG.
Still not sure?
Send us a description of your part — what it does, where it lives, what it has to survive — through our contact form and we'll recommend a filament for free.