PA11 usually offers the more forgiving impact response, while PA12 is generally easier to specify when a part must retain holes, clearances, and mating dimensions across changing humidity. The decision is not simply toughness versus stiffness: PA11 may survive an impact by deforming, whereas PA12 may be the better choice when the part must remain geometrically predictable after printing and conditioning.
The Better Fit by Part Requirement
Choose PA11 for clips, buckles, flexible covers, living hinges, repeated bending, and parts that must absorb impact without splintering. Choose PA12 for locating features, rigid housings, jigs, fixtures, bearing seats, sealed assemblies, and other parts where moisture-related dimensional movement could disturb a fit.
Neither polymer wins every mechanical comparison. A PA11 grade can be less suitable when permanent deformation is unacceptable, while a PA12 grade can be less suitable when a thin feature must flex through many cycles. Additives, print orientation, conditioning, and the manufacturing process can reverse a broad family-level expectation.
| Decision Point | PA11 | PA12 |
|---|---|---|
| Typical impact response | More likely to absorb energy through elastic and plastic deformation | Balanced impact resistance with less reliance on large deformation |
| Ductility | Usually the stronger candidate for high elongation and non-splintering behavior | Grade-dependent; many formulations remain tough but are commonly less extensible than comparable PA11 grades |
| Notched impact | Often favored, particularly for cold or impact-sensitive applications | Can perform well, but the result depends heavily on grade, notch geometry, temperature, and process |
| Repeated flexing | Usually better suited to clips, straps, buckles, and living-hinge-like features | Suitable for some flexible features, but bend radius and strain must be controlled more carefully |
| Moisture absorption | Low compared with short-chain nylons, but generally higher than PA12 | Usually the lower-moisture option within the PA11–PA12 comparison |
| Humidity-related property drift | Relatively controlled for a nylon, although stiffness and dimensions can still change | Usually offers more consistent behavior across dry and humid service conditions |
| Dimensional stability | Good when correctly processed and conditioned | Normally preferred for tight clearances and moisture-sensitive tolerances |
| Dry stiffness | Often overlaps with PA12; polymer name alone does not establish which printed grade has the higher modulus | |
| Thin impact-loaded walls | Can flex and distribute the load before fracture | May retain the original shape better under moderate loading, but local strain concentrations require attention |
| Press fits and locating holes | Usable when the design allows conditioning and dimensional compensation | Usually the safer starting point when fit retention is the main requirement |
| Drying and storage | Both remain moisture-sensitive printing materials and should be handled according to the filament or powder supplier’s instructions | |
| Typical strength | Tensile values may overlap; impact resistance, elongation, fatigue, and dimensional movement are more useful selection criteria | |
| Main limitation | Surviving the load does not guarantee that the part will retain its original geometry | Lower moisture uptake does not guarantee better fatigue life or better survival of a sharp impact |
The Same Impact Can Produce Two Different Failures
Impact resistance is often treated as a single ranking, but a printed component can fail in several ways. It can crack immediately, split along a layer boundary, turn white around a stressed feature, remain bent after the load, or retain its shape while developing a small crack that grows later.
PA11 is commonly selected when continued function matters more than perfect shape retention. A flexible cover may dent, a buckle may open farther than intended, or a clip may temporarily distort without separating into fragments. Arkema reports that its Rilsan PA11 generally provides higher impact resistance than PA12 and cites a large low-temperature advantage in a notched Charpy comparison[a]. That is a useful family-level direction, not a universal multiplier that can be applied to every printed PA11 and PA12 product.
PA12 is not a brittle alternative. Many PA12 grades provide useful impact strength, including at low temperature. Its more compelling advantage in this comparison is that a part can combine toughness with lower moisture uptake and more predictable geometry. A housing that remains unbroken but shifts a connector opening by several tenths of a millimeter may still be unusable, so the preferred failure behavior depends on what the component must protect or locate.
When Deformation Is Acceptable
- Protective covers that may dent without exposing the contents
- Snap arms that must pass over a retaining feature
- Buckles and closures subjected to sudden opening loads
- Parts dropped during handling or field use
- Flexible guards that should not create sharp fragments
PA11 is usually the better starting point.
When Geometry Must Survive
- Sensor housings with aligned ports
- Press-fit inserts and locating pins
- Fixtures that establish a repeatable position
- Seal grooves and mating flanges
- Assemblies with narrow running clearance
PA12 is usually easier to control.
Impact strength is not tensile strength. A filament can have a high tensile strength yet perform poorly around a notch, repeated bend, layer boundary, or sharp internal corner. “Stronger” is only useful when the measured property and loading direction are named.
Moisture Enters the Decision Twice
Moisture affects PA11 and PA12 before printing and after the finished part enters service. These are related problems, but they should not be treated as the same failure.
Moisture Before Printing
A spool can absorb enough moisture to disturb extrusion even when the final polymer has relatively low equilibrium moisture uptake compared with PA6 or PA66. Wet filament may produce popping, surface pits, inconsistent extrusion, stringing, reduced layer quality, or internal voids. The exact symptom depends on the formulation, printer, exposure time, and processing temperature.
PA12’s lower moisture absorption does not make it a no-dry material. It may remain printable for longer under the same storage conditions, but an opened spool can still move outside the supplier’s recommended moisture range. PA11 should also be dried and printed from controlled storage when mechanical consistency matters.
Moisture After Printing
Once a part is installed, absorbed moisture can plasticize the polymer. The resulting part may become less stiff, more extensible, or slightly larger than it was in the dry state. This does not necessarily mean that the material has been damaged. It means the part is moving toward a different conditioned state.
PA11 already has relatively low moisture sensitivity for a polyamide, but PA12 normally provides the smaller humidity-driven change. Evonik describes PA12 as combining extremely low water absorption with high dimensional stability and impact strength, including low-temperature performance[b]. This makes PA12 attractive when the same assembly must operate through seasonal humidity changes without a new clearance or fit problem.
Do not compare a freshly dried test bar with a conditioned production part. A dry PA11 sample can appear stiffer than it will be after weeks in a humid environment. The relevant comparison is the condition in which the finished component will actually be measured, assembled, and used.
Dimensional Stability Is a Three-Stage Problem
PA12 is often called the more dimensionally stable option, but moisture absorption is only one part of the result. Printed dimensions can change during cooling, during environmental conditioning, and during long-term loading. Selecting PA12 addresses only part of that chain.
1. Cooling and Crystallization
The part contracts as it cools, while semicrystalline regions develop within the polymer. Chamber temperature, toolpath, wall thickness, build position, and cooling rate can create different shrinkage in different directions.
2. Moisture Conditioning
The finished part absorbs moisture until it approaches equilibrium with its environment. PA12 generally limits this stage better, while PA11 may show more movement but still performs far better than many shorter-chain nylons.
3. Load and Creep
A dimension can continue to change under clamp pressure, bolt preload, spring force, or the weight of another component. Humidity and temperature can accelerate this movement even when the original print measured correctly.
This explains why higher dimensional stability does not automatically mean higher dry stiffness. Two grades can have similar tensile moduli while behaving differently after humidity exposure. A PA12 housing may retain a bore diameter more consistently even when a particular PA11 product has an equal or slightly higher dry modulus.
Part geometry can also dominate the polymer difference. A badly oriented PA12 bracket with uneven wall thickness may warp more than a well-designed PA11 part. Large flat surfaces, abrupt section changes, unsupported ribs, dense infill transitions, and thick bosses around thin walls can all create enough internal stress to hide the expected material advantage.
Published Impact Values Are Not Interchangeable
A material data sheet may list Charpy impact strength, notched Charpy strength, Izod impact strength, tensile elongation, or a statement such as “no break.” These results describe different loading conditions. A high unnotched result can coexist with a much lower notched result because the notch forces a crack to begin at one controlled location.
Temperature is equally important. A room-temperature test does not establish performance in a freezer, winter vehicle, cold warehouse, or high-altitude enclosure. Dry and conditioned specimens can also produce different outcomes because absorbed moisture changes the polymer’s deformation behavior.
Additive manufacturing introduces another variable: orientation. EOS lists 30% strain at break in the X and Y orientations and 25% in Z for its PA 1100 laser-sintered PA11 under the stated process conditions[c]. Its PA 2200 PA12 sheet lists 18% in X and Y but 4% in Z for that product and parameter set[d]. These figures illustrate why PA11 is associated with ductility and why build direction can dominate a PA12 result, but they should not be transferred directly to unrelated FDM filaments.
Before using a data-sheet number, match all five conditions: test method, notch condition, specimen temperature, moisture condition, and manufacturing orientation. A sixth check is needed when comparing commercial products: confirm whether either material contains plasticizer, impact modifier, glass fiber, carbon fiber, flame retardant, or another additive.
Commercial PA11 and PA12 filaments are not guaranteed to represent neat polymer behavior. A flexible PA12 formulation may outperform a rigid PA11 blend in repeated bending. A carbon-fiber PA11 can become much stiffer but lose the high elongation normally associated with unfilled PA11. A glass-filled PA12 may improve fixture stability while becoming less suitable for a snap arm.
Geometry Decides Whether PA11 Flexibility Helps or Hurts
The same flexibility that protects a PA11 component from fracture can create a problem in a dimension-sensitive assembly. The useful question is not whether flexibility is desirable in general, but which section of the part is allowed to move and which section must remain fixed.
| Part Feature | Better Starting Point | Reason | Condition That Can Change the Choice |
|---|---|---|---|
| Repeatedly opened snap arm | PA11 | Higher elongation and a more forgiving bend response can reduce crack initiation at the root | A modified flexible PA12 grade may work when the strain is low and the arm is long |
| Living-hinge-like strap | PA11 | Better suited to repeated flexing when the bend radius and print direction are controlled | Neither material compensates for a sharp crease or a layer boundary placed across the hinge |
| Press-fit metal insert | PA12 | Lower humidity-related dimensional movement helps retain the intended interference | PA11 may be preferred when impact or repeated removal matters more than fixed interference |
| Sealed electronics housing | PA12 | More stable flange, port, and seal-groove dimensions simplify assembly control | PA11 may suit a protective shell intended to deform during a drop |
| Thin protective cover | PA11 | The wall can distribute a local impact instead of cracking immediately | PA12 may be better when cover deflection could contact an internal component |
| Inspection or assembly fixture | PA12 | Repeatable locating surfaces and hole spacing are normally more valuable than additional elongation | Filled grades may be needed when stiffness and creep control exceed what unfilled PA12 offers |
| Cold-weather buckle | PA11 | Low-temperature impact and flexing behavior often favor PA11 | The actual grade must be tested at the lowest service temperature |
| Bearing or bushing seat | PA12 | Lower moisture movement helps preserve running clearance and concentricity | Wear additives, lubrication, heat, and sustained load may matter more than the base polymer |
| Tool handle or impact grip | PA11 | Energy absorption and non-splintering behavior can be more valuable than a perfectly rigid response | Surface texture, wall design, and internal support can control the result as much as polymer choice |
A useful hybrid design can separate these requirements. The enclosure body can use thicker ribs and stable locating surfaces, while a long snap arm carries the required movement. This reduces the need to select an entire polymer system around one small flexible feature.
The Test That Reveals More Than a Dry Bench Sample
A dry tensile bar does not reproduce the most common PA11–PA12 decision: whether a finished part will still fit and survive after environmental exposure. A more revealing comparison combines dimensional conditioning with the actual mechanical event.
- Print PA11 and PA12 parts using the intended geometry, orientation, wall structure, and production settings rather than scaled-down generic coupons.
- Measure the dimensions that control function: hole diameter, pin spacing, flange flatness, snap-arm position, seal compression, and running clearance.
- Keep one set in the dry printed condition and condition another set in an environment representative of actual service.
- Repeat the dimensional measurements before assembly. Record movement by feature and direction rather than reporting one overall percentage.
- Assemble both sets and apply the real loading event, such as a drop, snap cycle, clamp load, vibration sequence, or low-temperature impact.
- Inspect for fracture, layer separation, permanent bending, stress whitening, loss of seal compression, and changes in the mating fit.
- Measure the part again after the event. A component that remains unbroken but loses alignment should not receive the same result as one that returns to its original dimensions.
This combined test often separates the materials more clearly than nominal tensile strength. PA11 may retain function after a harder impact but show more permanent movement. PA12 may produce the more repeatable fit before and after humidity conditioning but reach its strain limit sooner in a sharply flexed feature.
Original dimensional data should be collected after the same conditioning period used for assembly. Measuring every part immediately after drying can create a tolerance that exists during inspection but not during service.
Choosing by Failure Consequence
Practical Selection Matrix
Choose PA11 When
- The part must bend, buckle, or deflect without creating fragments.
- Repeated flexing matters more than retaining an exact unloaded shape.
- A drop or sudden impact is the expected failure event.
- Low-temperature toughness is part of the service requirement.
- The design contains clips, flexible guards, straps, or hinge-like sections.
- Some permanent deformation is less harmful than a crack or sudden separation.
Choose PA12 When
- Humidity-related dimensional movement must be kept low.
- Holes, slots, seal grooves, and mating surfaces control function.
- The part is a fixture, bracket, housing, locator, or precision assembly component.
- The same fit must be reproduced across changing storage and service conditions.
- Deflection could cause contact with an internal component.
- Balanced mechanical behavior is preferred over maximum elongation.
Either material can work when the loads are moderate, tolerances are generous, and the selected commercial grades have been tested in the actual print orientation.
Neither base polymer fully solves the problem when the component needs very high stiffness, minimal creep, tight dimensional control, and repeated impact resistance at the same time. A reinforced grade, geometry change, metal insert, elastomeric impact feature, or multi-part design may be more suitable.
Compare products rather than polymer names when one filament is filled, impact-modified, plasticized, or intended for a different processing temperature. PA11 versus PA12 describes the resin family; it does not replace the technical data for the spool being purchased.
Technical Sources and Documentation
- [a] Key Properties of Rilsan® PA11 (Used for PA11 impact resistance, low-temperature behavior, moisture response, and dimensional stability context.)
- [b] VESTAMID® (Used for the PA12 water absorption, dimensional stability, and low-temperature impact characteristics.)
- [c] PA 1100 Material Data Sheet (Used for the PA11 additive-manufacturing elongation and orientation example.)
- [d] PA 2200 Material Data Sheet (Used for the PA12 additive-manufacturing elongation and orientation example.)
