The Damp Secret That's Ruining Your Prints

Filament Is Thirstier Than You Think

Most 3D printing filaments are hygroscopic, which means they pull moisture straight out of the air. It happens slowly, but it never really stops. Once a filament has absorbed enough water, that moisture turns to steam the instant it hits your hot end, and steam inside melted plastic causes all sorts of trouble.

You'll usually notice it as crackling or popping sounds as you print, tiny bubbles or pitting on the surface, stringing that won't go away no matter what you tune, and a general drop in strength once the part is done. If your prints have gone from crisp to fuzzy for no obvious reason, damp filament is one of the first things worth checking.

Which Filaments Suffer Most

Not every material is equally sensitive, and this is where a lot of guesswork goes wrong.

• PLA is fairly forgiving. It absorbs moisture slower than most, but it isn't immune, and old or cheap spools left in a humid room will still degrade.

• PETG absorbs moisture more readily than PLA and is notably fussier about it. Wet PETG tends to show stringing and a rough, hazy surface finish rather than snapping.

• ABS is less hygroscopic than PETG in absolute terms, but it's far more sensitive to the effects, because ABS already needs careful temperature control to avoid warping and layer separation. Add trapped moisture and cracking or weak layers become much more likely.

• Nylon and TPU are the thirstiest of the common materials by a wide margin, and even a few hours in humid air can noticeably harm a nylon print.

Keeping Below 20% Humidity

The rule of thumb among experienced printers is to keep filament storage under 20% relative humidity. Here's what actually helps:

• Store spools in sealed containers or resealable bags with a good dose of silica gel desiccant, and swap or recharge the desiccant regularly rather than leaving it forgotten in the bag.

• A cheap hygrometer inside your storage box tells you the truth instead of a guess. If it creeps above 20%, it's time to dry the filament or refresh the desiccant.

• If a spool has already absorbed moisture, most filaments can be dried out in a food dehydrator or a dedicated filament dryer at a low, sustained temperature for several hours. PETG and nylon in particular benefit from a proper drying session before a big print.

• Buy filament in smaller amounts if you print occasionally, so spools aren't sitting open for months at a time.

Once you've got your filament dry and consistent, it's worth locking in the rest of your settings too. The Filament calibration tool helps you tune lithophane thickness to a specific filament, and Calibration prints can help you check temperature and bridging behaviour so you know exactly how your dried filament performs on your printer.

Dry filament won't fix every printing problem, but it removes one of the most common and least visible causes of bad prints. Give your spools a proper home, and see the difference in your next print.