Both are polyamides, both are tough, both want an enclosure and a dry box, and both will punish carelessness. The difference between them is stability — dimensional and mechanical — and it is comfortably worth the roughly quarter-higher price per kilogram if your part has to fit anything.
Shrinkage is the first fork
Unfilled PA6's stored range is 0.8 to 2.0%, the largest of any common filament and the reason so many people conclude nylon is unprintable. PA12 runs 0.5 to 1.2%.
Applied to a 150 mm part at the top of each range: PA6 finishes at 147 mm and needs a 3.0612 mm correction to land on size. PA12 finishes at 148.2 mm and needs 1.8219 mm. A millimetre and a quarter of difference on a 150 mm part is the whole practical case for PA12 in anything that has to bolt to something else. Feed the shrinkage calculator a percentage and it returns the dimension to draw, so walking PA6's band from 0.8 up to 2.0 shows how much of the gap is chamber conditions rather than chemistry.
Both are large corrections, and neither material is one you compensate confidently on the first attempt. But the ranges matter as much as the midpoints: PA6's spread of over a percentage point across a 150 mm part is more than a millimetre of uncertainty, and that uncertainty is what actually stops you designing a fit.
The practical consequence is that warping follows shrinkage. PA6 lifts off the plate on parts where PA12 stays down, and the two behave differently enough that a chamber temperature tuned for one is not tuned for the other.
Water in service, which is the part people forget
Both nylons absorb moisture from the air. PA6 absorbs considerably more, because its shorter repeat unit means a higher density of the polar amide groups that hold water.
The consequence is not just a printing problem — it is a service problem. A PA6 gear that fits when installed will grow and soften over weeks in a damp environment; the same gear in PA12 moves far less. The stored note is direct: PA12 absorbs far less water than PA6 while still needing drying before a long print.
If the part is a bushing, a gear, a threaded fitting or anything that mates with metal, this is the decision, and it points at PA12 regardless of price.
What PA6 gives you for the money
Do not read the above as a dismissal. PA6 is the stronger and stiffer of the two, at 50–80 MPa tensile against PA12's 40–60, and the stored weakness list for PA12 names softness explicitly.
For a part that is loaded rather than fitted — a tool handle, a lever, a bracket that bolts on with clearance holes — PA6's extra stiffness is real, and its $35–70 per kilogram against PA12's $45–90 is a meaningful saving on a material this expensive.
PA6 is also more widely stocked, in more colours and more filled variants. If you want carbon fibre, glass fibre or a specific colour, the PA6-based product is the one that will exist.
A kilogram of PA12 goes noticeably further
Nylon 12 is one of the lightest filaments sold, at 1.00 to 1.04 g/cm³ against PA6's 1.12 to 1.15. Across a kilogram of 1.75 mm filament that is 411.64 m against 364.69 m — 46.94 m more, because PA6's 12.871% higher density costs it 11.404% of its length. The length and weight converter will do it for whatever density your data sheet gives.
The same effect runs through every part you print: an identical model in PA12 weighs about an eighth less than in PA6. On a spool basis PA12 is roughly a quarter dearer; on a parts basis the gap is smaller than that, and for anything where mass is a design constraint — a drone frame, a moving carriage, a wearable — PA12 is lighter as well as more stable.
They print at almost the same settings
One thing that does not separate them is the profile. Both want 250–275 °C at the nozzle — PA6 stretches a little higher, to 280 — a bed between 60 and 90 °C, an enclosure, and drying at 80 °C for 8 to 12 hours.
The one practical difference on the machine is bed adhesion. PA6 essentially requires garolite or a polyamide-specific sheet; PA12's stored note says it is more forgiving on textured PEI, which for someone without a specialist plate can be the deciding factor before any of the material properties are considered.
PA612, the copolymer nobody mentions
There is a third option that splits the difference by design. Nylon 6/12 sits between the two on density, on shrinkage at 0.6 to 1.4%, and on water uptake, while keeping tensile figures of 45–70 MPa close to PA6's.
It exists precisely for parts that want PA6's toughness with less moisture movement — wear parts, bushings, anything running against a shaft. Its drawbacks are availability and price, both of which sit near PA12's. If you can find it, it is frequently the right answer and it is skipped because it is the least famous of the three.
Choosing
- The part mates with something bought or machined — PA12, or PA612.
- The part will live somewhere damp — PA12.
- The part is loaded and has clearance everywhere — PA6, and enjoy the saving.
- The part is large and flat — PA12 for the lower warping, or a filled PA6, which reduces shrinkage far more than either unfilled option.
- Mass is a design constraint — PA12.
And whichever you pick, the practical advice from nylon against PETG still stands: unfilled nylon of any kind is a difficult material on a desktop machine, and for anything sizeable a fibre-filled grade is not an upgrade so much as the version that works.