How strong is PLA? Stronger than most people expect. Printed solid, it yields at about 50 to 60 MPa in tension, according to filament manufacturers’ datasheets. That is enough for many brackets, jigs, and housings.
The number alone is misleading, though. PLA is brittle, it is much weaker across its layers than along them, and it softens at about 55 to 60 °C. Whether PLA is strong enough depends far more on those three limits than on the headline strength. This guide gives the numbers, shows what they mean for a real part, and explains when to choose another material.
PLA Strength in Numbers
These values come from two manufacturers’ technical data sheets. Both tested specimens printed at 100% infill.
| Property | UltiMaker PLA | Prusament PLA |
|---|---|---|
| Tensile yield strength, printed flat | 52.5 MPa | 51 MPa |
| Tensile yield strength, printed on edge | 59.0 MPa | 59 MPa |
| Tensile strength, pulled across the layers | 33.1 MPa (breaks without yielding) | Not listed |
| Stiffness (tensile modulus), printed flat | 3.25 GPa | 2.3 GPa |
| Elongation at break, printed flat | 7.8% | Not listed |
| Elongation at break, across the layers | 2.0% | Not listed |
| Flexural strength, printed flat | 96.8 MPa | 83 MPa |
| Heat deflection temperature at 0.45 MPa | 58.8 °C | 55 °C |
For comparison, the raw resin many filaments are made from, NatureWorks Ingeo 4043D, is listed at 60 MPa tensile yield strength with a glass transition of 55 to 60 °C. A well-printed part gets close to the resin’s strength in its best direction.
To put the figures in context, 52 MPa is about one fifth of the yield strength of 6061-T6 aluminium, and PLA is about twenty times less stiff. A PLA part can replace a metal one only if it is made much thicker or the load is light.
What the Numbers Mean for a Real Part
Take a solid PLA strap 10 mm wide and 4 mm thick, pulled along its length. Its cross-section is 40 mm².
force at yield = strength x area
printed flat (load along the layers):
52.5 MPa x 40 mm^2 = 2,100 N (about 214 kg)
printed upright (load across the layers):
33.1 MPa x 40 mm^2 = 1,324 N (about 135 kg)The same part, in the same material, loses about 37% of its strength because of the direction it was printed in.
Those are failure loads for a perfect specimen in a short test at room temperature. A real part needs a margin. With a safety factor of 3, the working loads become about 700 N (71 kg) and 440 N (45 kg). How to choose a safety factor is covered in our guide to predicting mechanical failure with FEA.
The example also assumes a solid part in pure tension. Most printed parts are not solid and are loaded in bending, where stress is several times higher for the same force.
The Three Limits That Matter More Than Strength
1. Layer direction
A printed part is a stack of layers bonded together, and the bond is weaker than the plastic itself. In the UltiMaker data, a specimen pulled across its layers broke at 33.1 MPa, against 52.5 to 59.0 MPa for specimens loaded along the layers. It also broke at 2.0% elongation without yielding first.
This is why a printed hook or clip snaps cleanly along a layer line. Orient the part so the main load runs along the layers, not across them.
2. Brittleness
PLA stretches very little before it breaks. Under a steady load this is fine. Under impact, a sharp knock, or a snap-fit that has to flex, PLA cracks where a tougher plastic would bend. Sharp internal corners make it worse, because stress concentrates there.
3. Heat
PLA’s heat deflection temperature is 55 to 59 °C in the datasheets above, and its glass transition is about the same. Near that temperature a loaded part sags and stays deformed. A car parked in the sun, a spot next to a motor, or a dishwasher can all get hot enough.
PLA also deforms slowly under a load that is held for a long time, even at room temperature. A part that passes a quick pull test can still creep out of shape after weeks under the same load.
How to Make a PLA Part Stronger
- Orient for the load. Put the main tensile and bending stresses along the layers.
- Add walls before infill. In bending, most of the load is carried by the outer skin. Extra perimeters usually add more strength than extra infill for the same amount of plastic.
- Use enough infill for the job. Datasheet values are for 100% infill. A sparse part is weaker than those numbers suggest.
- Print hot enough for good bonding. Layers that fuse well are stronger across the layer lines. Too cold a nozzle or too much cooling weakens that bond.
- Round the internal corners. A fillet spreads the stress that a sharp corner concentrates.
- Make it thicker where it bends. Bending strength rises with the square of the thickness, so a small increase goes a long way.
If the part matters, a design-for-3D-printing review will catch orientation and wall-thickness problems before printing.
When PLA Is Enough, and When It Is Not
| Use | PLA suitable? | Why |
|---|---|---|
| Jigs, fixtures, and drill guides used indoors | Yes | Stiff, accurate, steady light loads |
| Enclosures and covers away from heat | Yes | Low load, room temperature |
| Brackets holding light, steady loads indoors | Yes, with a margin | Watch print direction and creep |
| Prototypes for fit and form | Yes | Cheap and dimensionally accurate |
| Parts near motors, heaters, or in vehicles | No | Softens at about 55 to 60 °C |
| Snap-fits, hinges, and parts that take impact | No | Too brittle |
| Parts under a heavy load held for months | No | Creeps over time |
| Outdoor parts in sun and heat | No | Heat is the main problem |
| Anything where failure could injure someone | No | Printed strength varies too much to rely on |
When PLA falls short, PETG and ABS are the usual next steps. See PLA vs ABS vs PETG for a side-by-side comparison, or the material selection guide to choose by requirement.
Frequently Asked Questions
How much weight can PLA hold?
It depends on the shape, the print direction, and how the load is applied. As a reference point, a solid 10 mm by 4 mm PLA strap pulled along its layers yields at about 2,100 N, or roughly 214 kg, in a short test. A safe working load is a fraction of that, and far less if the part bends or is loaded across its layers.
What is the tensile strength of PLA?
Manufacturer datasheets list a tensile yield strength of about 51 to 59 MPa for specimens printed solid and loaded along the layers. Pulled across the layers, one datasheet reports 33 MPa.
Is PLA stronger than PETG or ABS?
PLA is stiffer and holds its shape well under a steady load, but it is more brittle and far less heat resistant. PETG and ABS bend further before breaking, which often makes them the better choice for parts that flex or take knocks.
Does PLA need 100% infill to be strong?
No. For most parts, more walls and a moderate infill give most of the strength with less plastic and time. Use 100% infill for small, highly loaded parts or where the datasheet strength is needed.
Does PLA get weaker over time?
Indoors, at room temperature and without load, PLA parts last for years. Under a constant load it slowly deforms, and heat speeds that up sharply.
Need a Printed Part That Has to Carry Load?
RunTechEngineer offers functional part printing and can advise on material and print orientation for your design. See our full 3D printing services, or contact us with your model and how the part will be used.
