PETG vs PLA Strength Comparison: What the Datasheets Show

Most petg vs pla strength comparison articles repeat the same two lines: PETG is “tougher,” PLA is “more rigid,” and neither claim gets a number attached. Prusa Polymers publishes matched technical datasheets for Prusament PETG and Prusament PLA, both tested on the same printer (Original Prusa i3 MK3), the same slicer, and the same ISO methods (ISO 527-1 for tensile, ISO 178 for flexural, ISO 179-1 for Charpy impact). That’s about as close to apples-to-apples as filament data gets, and the numbers don’t fully back up the marketing shorthand.

Tensile strength: closer than the reputation suggests

On raw filament (unprinted, pulled per ISO 527), PLA comes in at 57 ± 1 MPa tensile yield strength versus PETG’s 46 ± 1 MPa. That gap looks decisive until you print actual test bars. On printed specimens, PETG lands at 47 ± 2 MPa printed flat and 50 ± 1 MPa printed on edge (vertical XZ); PLA prints at 51 ± 3 MPa flat and 59 ± 2 MPa on edge. PLA still wins on pure tensile yield, but the margin in printed parts (about 8-9 MPa) is a lot narrower than the “PLA is way stronger” framing implies.

Where the two actually diverge is stiffness, not strength. PLA’s tensile modulus is 2.3-2.4 GPa against PETG’s 1.5-1.6 GPa, and PLA’s elongation at yield is only 2.9-3.2% compared to PETG’s 5.1%. PLA is the stiffer material that resists deformation up to a point, then yields with less warning. PETG stretches further before it gets there. If your part needs to hold a precise dimension under light load, PLA’s higher modulus is the relevant number, not tensile strength.

Impact strength: this is where PETG earns its reputation

Charpy impact testing is where the two materials split hardest. On the unnotched Charpy test, PETG specimens didn’t break at all, in either print orientation. PLA specimens did break, registering 13 ± 1 kJ/m² (flat) and 14 ± 1 kJ/m² (on edge). Notch a PETG specimen first and it breaks too, at 6 ± 1 kJ/m² flat and 3 ± 1 kJ/m² on edge; Prusa doesn’t list a notched value for PLA at all.

That pattern matches what’s documented more broadly in FDM literature: PLA tends to fail abruptly through brittle fracture, while PETG deforms before it finally lets go. The PMC study on PET-G and PLA processing parameters reinforces this indirectly through its process sensitivity data (below), but the Prusament unnotched-vs-notched contrast is the cleanest single data point: PETG’s toughness advantage is real and it’s specifically an impact/toughness property, not a tensile-strength property.

The number that actually predicts layer failures

Interlayer adhesion is the property that decides whether a functional part delaminates under load, and it’s the one most comparison posts skip. Prusa’s own testing puts PETG interlayer adhesion at 18 ± 4 MPa and PLA at 17 ± 3 MPa. That’s within each other’s error bars. If you’ve read that PETG bonds layers dramatically better than PLA, this vendor’s own numbers don’t support “dramatically” — they support “roughly the same, printed correctly.” Print quality (nozzle temperature, cooling, and part cooling fan speed) will move interlayer adhesion further than switching material will.

Orientation, infill, and temperature move the numbers more than the material choice

A 2022 study on FDM PET-G and PLA processing parameters tested how print settings affect specific tensile strength (strength normalized for part weight) across both materials and found the process variables matter as much as the resin choice. Raising nozzle temperature increased specific tensile strength for both materials, but the effect was more than double for PLA (a 27.53% increase) compared to PETG (12.69%). Infill density pushed absolute tensile strength up for both — 37.27% for PLA and 24.42% for PETG at maximum infill — while cutting the strength-to-weight ratio in both cases, since added plastic mass outpaces the strength gain. Print orientation had the largest swing of any variable: parts printed flat (XY) consistently outperformed parts printed on edge (XZ), and PLA showed a bigger orientation penalty (58.21% variation) than PETG (29.29%).

The practical read: a petg vs pla strength comparison done at default slicer settings and one done at a tuned, temperature-optimized, high-infill profile can produce noticeably different rankings. PLA gains more from a good profile than PETG does, and loses more from a bad one.

Print settings behind these numbers

Prusa’s datasheets list the exact recommended settings used to generate the results above:

• PETG: nozzle 250 ± 10°C, bed 80 ± 10°C, cooling fan 50%, up to 200 mm/s
• PLA: nozzle 210 ± 10°C, bed 40-60°C, cooling fan 100%, up to 200 mm/s

PETG also has a materially higher heat deflection temperature (68°C at both 0.45 and 1.8 MPa load) versus PLA (55°C), which matters more than either tensile number if the part sits somewhere warm — a car dashboard mount, a lampshade near an incandescent bulb, or an enclosure over anything that generates heat.

Picking one for a given part

For anything that takes a drop, a snap-fit, or repeated flex — brackets, hinge clips, phone mounts, outdoor fixtures — PETG’s impact behavior and higher heat deflection temperature are the deciding factors, not tensile strength. For dimensionally precise, stiff parts printed indoors at room temperature — jigs, enclosures, most Etsy-shop decorative and functional prints — PLA’s higher modulus, easier bed adhesion, and lower nozzle/bed temps make it the more practical default. Neither material is “stronger” in every sense that matters; they trade tensile yield for toughness and stiffness for ductility, and the print settings you actually use move those numbers more than the datasheet implies.

Two settings dominate that gap. PETG is hygroscopic enough that a damp spool will undercut every number above, which the filament drying protocol covers, and both materials change behaviour with ambient temperature, listed per material in the chamber temperature reference. Larger PETG parts also lift at the corners more readily than PLA, and the ranked fixes for that are in why prints warp at corners.

FAQ

Is PETG stronger than PLA?

Not on tensile strength. Prusa’s matched datasheets put printed PLA at 51 ± 3 MPa flat and 59 ± 2 MPa on edge, against PETG’s 47 ± 2 MPa flat and 50 ± 1 MPa on edge. PETG wins on toughness instead: in unnotched Charpy impact testing PETG specimens did not break at all in either orientation, while PLA broke at 13 to 14 kJ/m². The two trade tensile yield for impact resistance.

Does PETG have better layer adhesion than PLA?

Barely, and not enough to matter. Prusa’s own testing puts PETG interlayer adhesion at 18 ± 4 MPa and PLA at 17 ± 3 MPa, figures that sit inside each other’s error bars. The common claim that PETG bonds layers dramatically better is not supported by that data. Nozzle temperature, cooling, and part-cooling fan speed move interlayer adhesion further than switching material does.

Does PETG handle heat better than PLA?

Yes, and by a margin that often decides the material choice on its own. PETG’s heat deflection temperature is 68°C at both 0.45 and 1.8 MPa load, against 55°C for PLA. For a part that sits somewhere warm, such as a car dashboard mount, a lampshade near an incandescent bulb, or an enclosure over heat-generating electronics, that 13-degree gap matters more than either tensile figure.

Does print orientation matter more than material choice?

Orientation produced the largest swing of any variable in a 2022 study of FDM processing parameters. Parts printed flat in XY consistently outperformed parts printed on edge in XZ, and PLA showed a far larger orientation penalty at 58.21 percent variation against PETG’s 29.29 percent. Nozzle temperature also moved specific tensile strength more than twice as much for PLA as for PETG.

Which filament should be used for functional parts?

It depends on the load type rather than a general strength ranking. Parts that take drops, snap-fits, repeated flex, or outdoor heat, such as brackets, hinge clips, and phone mounts, favour PETG for its impact behaviour and higher heat deflection temperature. Dimensionally precise indoor parts such as jigs and enclosures favour PLA for its higher tensile modulus, easier bed adhesion, and lower nozzle and bed temperatures.

Cost, and the Decision Above This One

The two materials are close enough in spool price that cost rarely decides between them on its own, but the part cost can differ more than the spool cost suggests, because PETG’s higher printing temperatures and typically slower speeds change the electricity and machine-time side of the total. The print time and filament cost estimator prices the same model in either material with its density and speed ceiling already applied, which is a better basis for the comparison than the price per kilogram.

There is also a decision sitting above this one. If the part’s requirement is fine surface detail rather than mechanical strength, neither filament is really the answer and the question becomes a process choice rather than a material choice — that trade is worked through in the FDM vs resin decision framework.

Whichever material you settle on, the strength figures above only hold if the printer is actually extruding what the slicer asked for. Layer bonding in particular is sensitive to under-extrusion and to melt temperature, so run the sequence in the 3D printer calibration order before drawing conclusions from a part that broke.