PETG PETG (polyethylene terephthalate glycol-modified), including translucent and tough PETG

PETG is a glycol-modified version of PET, the plastic used in drink bottles. The glycol modification keeps it from crystallizing, which makes it easy to print and gives it good clarity in natural and translucent grades. For buyers, PETG is the practical step up from PLA: tougher, more forgiving under impact and flexing, more tolerant of warmth and moisture, and still affordable.

It sits between PLA and the engineering plastics. QIDI's comparison table lists a heat deflection temperature (HDT, the temperature at which a standard bar sags under a light 0.45 MPa load) of 72.9 °C for PETG Basic, compared with 55.3 °C for PLA Basic and 93.0 °C for ASA, all as printed. That extra margin over PLA is often exactly what an everyday functional part needs, but it isn't enough for a dashboard or a hot engine bay.

Variants include standard PETG, high-speed PETG (QIDI PETG Rapido), tougher blends (QIDI PETG-Tough, which QIDI lists at 42.7 MPa between layers) and translucent PETG, which QIDI rates the same as PETG Basic. Carbon- and glass-fiber PETGs are covered on the PETG-CF page.

PETG's main strength is toughness. It's less stiff than PLA, so it bends a little under load, but that same give means it absorbs impacts and flexing that would crack PLA. QIDI lists PETG Basic at 45.2 MPa tensile strength and 68.3 MPa bending strength along the layers. In practice, a PETG bracket that's overloaded tends to bend or yield rather than shatter, which is usually the safer way for a part to fail.

Layer adhesion is very good. All FDM parts are anisotropic, meaning weaker between layers (Z) than along them, but PETG fuses strongly to itself: QIDI gives 37.52 MPa Z tensile for PETG Basic and 42.7 MPa for PETG-Tough, both higher than the 32.46 MPa QIDI lists for PLA Basic. That makes PETG a good choice for parts that can't be oriented ideally. We still orient parts so the main loads run along the layers.

PETG creeps under sustained load less than PLA but more than engineering plastics, and creep increases as temperature rises. For a clamp or bracket that holds force continuously, PETG is a reasonable everyday choice; for long-term high loads or warm environments, consider PETG-CF, ABS, ASA or nylon. PETG is also notch-sensitive: sharp inside corners concentrate stress, so design in fillets.

QIDI rates PETG Basic and PETG Translucent at 72.9 °C HDT, and PETG Rapido and PETG-Tough at 70.0 °C, all at 0.45 MPa and as printed. The PETG Basic product page gives 71.8 °C without stating the load. Under heavier loads, softening starts lower, so we treat PETG as comfortable in warm rooms, workshops and sheltered outdoor spots, but not for parts that run hot.

QIDI does not generally recommend annealing PETG, and we don't anneal it. If you need more heat resistance, the next steps are ABS or ASA (QIDI lists ASA at 93.0 °C HDT at 0.45 MPa), then PC and the fiber-filled engineering materials.

PETG holds up to weather better than PLA: it doesn't absorb much water, and it tolerates sun for longer. Over extended exposure, though, it can yellow (especially natural and translucent grades), lose gloss and become less tough. A UV-resistant paint or coating helps opaque parts. For parts that will live outdoors permanently, we'd usually recommend ASA, which is formulated for UV stability.

PETG has generally good chemical resistance for an everyday plastic. It handles water, dilute acids and alkalis, many household cleaners, and generally oils and greases well. Brief contact with isopropyl alcohol (IPA) is generally fine, though repeated soaking can haze or craze clear parts.

Strong solvents are a different story. Acetone and some aromatic solvents can attack PETG, and fuels and brake fluid are best avoided or tested first. Sunscreen and insect repellent can stress-crack some plastics under load, so if your part will be handled with these, ask us about a test sample. Overall, PETG is a better choice than PLA for chemical exposure, and nylon is better still for many harsh chemicals.

PETG resists moisture well once printed. QIDI lists PETG Basic and Translucent at 0.05 % saturated water absorption, though it lists PETG-Tough at 0.46 %, so values vary by grade and test. Finished parts don't swell or soften noticeably in humid or wet conditions, which is one reason PETG works well for bathrooms, gardens and workshops.

The filament itself is mildly hygroscopic (it absorbs moisture from the air), and damp PETG prints with more stringing, bubbles and weaker layers. QIDI treats drying as optional, but we dry PETG before printing as standard practice, because consistent dry filament gives cleaner surfaces and better strength.

PETG prints with a glossy finish that looks clean and slightly 'wet'. Layer lines are visible but softened by the gloss. Detail is good but not as crisp as PLA: sharp corners round a little, and fine text and small features are softer, which is why we rate it lower for detail.

Stringing is PETG's signature cosmetic issue. PETG is sticky and stringy when molten, so fine wisps or small blobs can appear between features, especially on parts with many separate islands such as grilles or text. We tune settings and dry the filament to minimize this, and remove strings during finishing, but very intricate PETG parts may show some small marks.

Translucent PETG transmits and diffuses light rather than being glass-clear. Infill patterns, layer lines and internal walls show through, which can look attractive in lamp shades and diffusers. For maximum light transmission, we print with thicker solid walls and fewer internal structures. Tell us if appearance in backlight matters, as it changes how we prepare the part.

PETG is harder to sand and paint than PLA or ABS. It's tough and slightly gummy, so sanding tends to fuzz the surface rather than leaving it smooth, and paint needs a proper primer for adhesion. Most PETG parts are best used as printed. Vapor smoothing isn't something we offer for PETG, and we don't anneal it.

PETG sticks extremely well to some build surfaces. On smooth PEI it can bond so strongly that it pulls chips out of the plate, and in rare cases leaves a rough patch on the bottom face of your part. We use textured plates or a release layer to prevent this, which gives the bottom face a slightly textured finish. If the underside is cosmetically important, let us know.

Heat-set inserts work well in PETG, and it can be glued with cyanoacrylate or epoxy, though the joint is weaker than with PLA or ABS because PETG is chemically resistant. Mechanical fastening is often more reliable for assemblies.

PETG shrinks a little more than PLA but much less than ABS, and it warps very little, so large parts print flat without an enclosure. Overall dimensional accuracy is good for functional parts. Holes print slightly undersized, and the softer edges mean small features are a little less precise than in PLA.

PETG's slight flexibility helps with fits: press-fits and snap-fits that would crack PLA often work in PETG. For precise sliding fits, design in clearance, as PETG's surface can be grippy, and test critical fits on one sample before ordering a batch.