Key takeaways
- Popping, stringing, a rough matte surface and weak layer bonds are the four signs of a wet spool.
- Dry 10–15 °C below the material's glass transition. Hotter fuses the coils together and ruins the spool.
- Nylon absorbs enough water in an open room in a single afternoon to change how it prints.
- Drying is a repair. Storage is the fix: sealed box, indicating desiccant, and a heated dry box for hygroscopic grades.
Every polymer we sell absorbs water from the air. Some do it slowly enough that you can ignore it for weeks; nylon does it fast enough to change the print between the morning and the afternoon. What follows is what actually happens, how to spot it, and the numbers we ship on every Material Passport.
What water does inside the nozzle
Absorbed moisture sits between the polymer chains. In the melt zone it flashes to steam, which does three things: it blows the extrusion apart into a foamed, furry bead, it disrupts pressure control so flow becomes uneven, and it hydrolyses some polymers — polyesters and polyamides especially — permanently shortening the chains and lowering strength.
A wet nylon part can lose a third of its tensile strength. That loss is not recoverable by drying the part afterwards.
Four signs your filament is wet
- Popping, hissing or crackling at the nozzle. This is steam escaping. It is the least ambiguous sign there is.
- Stringing and blobs that persist after you have tuned retraction and lowered temperature.
- A rough, matte, slightly furry surface where the same spool used to print smooth — with a diameter that measures fine.
- Layers that peel apart in a part that used to hold. Water interferes with the weld between layers.
Drying temperatures and times
Set the dryer 10–15 °C below the material's glass transition temperature. Below that you drive out water; above it the coils soften, weld together, and the spool becomes unusable — which is the single most common way people destroy filament while trying to save it.
| Material | Temperature | Time | Storage after |
|---|---|---|---|
| PLA | 45 °C | 4 h | Sealed box with desiccant |
| PETG | 65 °C | 6 h | Sealed box with desiccant |
| ABS / ASA | 70 °C | 4 h | Sealed box with desiccant |
| TPU 95A / 85A | 55–60 °C | 6 h | Sealed box with desiccant |
| PA12 / PA-CF | 70 °C | 8–12 h | Heated dry box while printing |
| PA6-GF | 80 °C | 12 h | Heated dry box while printing |
| PC | 80 °C | 8 h | Heated dry box while printing |
How to dry a spool
- 01
Check the spool material, not just the filament
Some cheap spools are moulded from PLA or PS and will sag at 70 °C even when the filament is fine. Transfer the filament to a metal or PC spool, or dry at 55 °C for longer.
- 02
Set the temperature from the table, not from the dial preset
Dryer presets are often optimistic. If you are using a kitchen oven, verify the real temperature with a separate thermometer — domestic ovens routinely overshoot by 20 °C, which is enough to fuse a spool.
- 03
Run it for the full time with airflow
Water has to leave the enclosure, not circulate in it. A dryer with a vent or a slightly open oven door removes far more moisture than a sealed box at the same temperature.
- 04
Move it straight into dry storage
A dried nylon spool left on the bench is measurably wet again within hours. Go directly from the dryer to a sealed box with fresh desiccant, or to a heated dry box that feeds the printer.
- 05
Print from the dry box for hygroscopic grades
For nylon, PC and carbon-filled grades, keep the spool in a heated dry box at 50–60 °C during the print. On a 12-hour print this is the difference between the first layer and the last layer having the same properties.
Storage is the actual fix
Drying is a repair for a storage failure. The materials that need drying most are the ones that need storing best.
- Use indicating desiccant. Silica gel that changes colour tells you when it is saturated. Uncoloured gel that has been in the box for a year is doing nothing.
- Regenerate, do not replace. Most indicating silica gel recovers fully at 120 °C for two hours.
- Sealed box beats vacuum bag for spools in rotation, because you will open a bag and not re-seal it properly.
- Aim under 20 % relative humidity inside the box. A cheap hygrometer costs less than one ruined nylon print.
Every ZORVA spool ships with its drying schedule printed on the Material Passport, and hygroscopic grades ship in a resealable bag with indicating desiccant already inside.
Frequently asked
What temperature should I dry filament at?
Set 10–15 °C below the material's glass transition: 45 °C for PLA, 65 °C for PETG, 70 °C for ABS, ASA and most nylons, 80 °C for PA6-GF and polycarbonate. Going hotter softens the coils, which welds the spool together and ruins it.
How long does it take to dry filament?
Four hours restores a mildly damp PLA or ABS spool. PETG and TPU need around six. Nylon and polycarbonate need 8–12 hours, and a spool that has been open in humid air for weeks may need a second cycle.
Can I dry filament in a kitchen oven?
Yes, with care. Verify the real temperature with an independent thermometer, because domestic ovens commonly overshoot by 20 °C and their lowest setting may already be above a safe drying temperature. Leave the door slightly ajar so moisture can escape, and never use a gas oven with an open flame for this.
How can I tell if my filament is wet?
Listen for popping or hissing at the nozzle, look for persistent stringing after tuning retraction, and watch for a rough matte surface on a spool that used to print smooth. Extruding 100 mm with the fan off and inspecting the strand for bubbles confirms it in under a minute.
Does drying filament restore a weak printed part?
No. Drying restores the filament, not parts already printed with it. Some hydrolysis in polyesters and polyamides is permanent, so a spool that printed badly for months may never reach its original strength even after a full drying cycle.