PA6 (nylon 6) is the polyamide you specify when toughness, flow into thin walls and as-moulded surface matter more than peak heat resistance. This page does not repeat the PA66 grade-family comparison: it answers one question — which parts belong in PA6 rather than PA66 — then how to buy PA6 once moisture, not the grade code, decides the numbers you get.
PA6 is not cheaper PA66: the two differ in water uptake, stiffness retention when hot and humid, and flow length. The PA66 category covers grade families; this page covers the boundary between them.
Unfilled PA6 keeps more elongation than the same part in PA66: clips, cable ties, latch arms, dropped housings.
PA6 runs cooler and fills further: where PA66 short-shots, PA6 often fills the same cavity. Confirm the window on the grade TDS.
PA6 reproduces the tool surface and takes colour evenly, so visible housings are specified in it.
Where service is mild and tolerances absorb moisture movement, PA6 usually costs less per part.
Step up to PA66 when the part carries sustained load near its service temperature, when a tolerance must hold in humid service, or when it sees hot water or glycol. Creep and hydrolysis go first.
| Decision point | PA6 | PA66 |
|---|---|---|
| Load case | Impact, snap-fit | Sustained load, creep |
| Dimensions | Moisture growth OK | Tight when humid |
| Geometry | Thin wall, long flow | Stiffness-driven |
| Finish | As-moulded | Painted, high-heat |
| Commercials | Unit cost | Failure cost |
Nylon absorbs moisture from air, and PA6 takes up more, and faster, than PA66. Every data-sheet number depends on the state it was measured in.
A fresh dry part is stiff and brittle; in service it absorbs water, gains toughness, loses stiffness. Design to conditioned values.
Absorbed water swells the part: press fits and snap-fit engagement shift after moulding, so a dry measurement can fail assembly later.
Moisture in the barrel causes hydrolysis, splay and brittleness. Agree time, temperature and dew point; keep pellets sealed.
Glass fibre raises stiffness and heat deflection, cuts elongation. In PA6 the toughness you chose it for erodes first.
Confirm loading by ash test, not compound name, and test the weld line: reinforced nylon fails there first.
Fibre aligns with flow, so shrinkage is directional and warpage follows gate position. See warpage causes and what GF30 changes.
Nylon loses molecular weight each heat history, and PA6 runs on a thin impact margin. Fix a maximum ratio, re-dry, require impact and viscosity at it.
Only if service temperature and tolerance allow. Shrinkage, moisture uptake and creep all change, so the part needs revalidation, not a swap.
Yes, and that is the practical difference: stiffness, strength and dimensions all move more. Require conditioned values before committing a tolerance.
Always — moisture causes hydrolysis and brittle parts. See the resin drying guide for time, temperature and dew point.
Less so. Each loading step trades elongation for stiffness; specify the lowest that passes and test the weld line.
Yes, with a stated maximum ratio, re-drying, and impact and viscosity measured at it.
Sourcing nylon 6? Send grade family, reinforcement, viscosity window and service medium to the plastic materials desk. Compare PA66 resin, POM acetal and engineering plastics, or send a drawing to custom molding services.
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