Nylon 6 and 66 absorb water from the air. As they do, parts grow slightly, get softer and lose stiffness, and fits that were perfect off the press can bind or loosen weeks later. It’s normal nylon behavior, and it can be designed around or avoided.
What’s happening
- Straight out of the press, nylon is dry. It then absorbs moisture until it balances with the surrounding humidity, which can take days to months depending on wall thickness.
- Absorbed moisture makes the part tougher and more flexible, but also slightly larger and less stiff.
- Nylon 6 and 66 absorb noticeably more than nylon 11 and 12.
Options
| Option | Effect |
|---|---|
| Measure conditioned parts | Check dimensions after conditioning, not straight off the press, so tooling is cut for the size the part will actually be. |
| Glass-filled nylon | Glass doesn’t absorb water, so growth and stiffness loss are much smaller. |
| Nylon 11 or 12 | Absorbs far less moisture. Nylon 11 & 12 |
| Acetal (POM) | Very low moisture uptake and excellent dimensional stability. Acetal |
| PBT | Low absorption; good for electrical parts. PET / PBT |
| Polyketone | Low uptake with nylon-like toughness. Polyketone |
Nylon 6 & 66 · Drying guide · Tell us the grade you run now →