How to store spools so they do not absorb moisture or tangle

Symptom

A spool that was in storage starts producing strings, bubbles or weak layers, or while printing it tangles and stops feeding because the filament end came loose when it was stored.

Likely causes, from most to least likely

1. Spool stored in the open: in a home at 55% humidity, freshly dried filament absorbs moisture again within 2-12 hours, according to Bambu Lab.
2. A bag or box that does not seal well, or spent desiccant.
3. Very hygroscopic materials (nylon, PP, PVA, BVOH, TPU) stored the same way as PLA.
4. Direct sunlight, heat or an air-conditioning vent nearby.
5. A loose filament end: the turns cross and a knot forms that ends up stopping the print.

Checks to tell which one it is

• Put a thermo-hygrometer in the box: Bambu Lab recommends below 20% relative humidity for most filaments; Elegoo, below 30% and 15-25 °C.
• Check that the bag or box seals well and the desiccant is still effective.
• Check whether the filament end is secured in the spool's holes.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Store sealed with desiccant

   Store each spool in its original bag with the desiccant, closed with a clip, or in a vacuum bag with desiccant (you can reuse the one it came with and put it in the centre of the spool). Keep it somewhere dry, dark and cool, away from sun, heat and air conditioning.

   Check: Humidity inside the bag or box stays low.

   If that does not fix it: For the most sensitive materials, use a dry box (next step).

2. Dry box for the most absorbent

   For nylon, PP, PVA, BVOH or TPU, use an airtight box with desiccant and a thermo-hygrometer, or dry them before every print (Prusa). If you can, print straight from the dry box. Check the desiccant regularly and replace it when it is no longer effective.

   Check: Prints come out the same at the start and end of the spool.

   If that does not fix it: Dry the spool before using it (next step).

3. Dry what has absorbed moisture

   If the spool has been left out, dry it at the maker's temperature. Elegoo suggests drying very hygroscopic filaments once a week and normal ones every 1-2 months or when symptoms appear. Creality recommends keeping PLA, PETG, ABS and ASA dry during printing when room humidity is above 50%, and always PC, TPU and PA.

   Check: Bubbles and strings disappear.

   If that does not fix it: If it still fails, look for other causes in the stringing or weak layer guides.

4. Do not dry in a kitchen oven without control

   Elegoo advises against microwaves and kitchen ovens, and Prusa warns that home ovens measure temperature poorly and can soften the filament and fuse the turns. Use a filament dryer or, if you use an oven, check it with an external thermometer.

   Check: The spool comes out dry with no fused turns.

   If that does not fix it: Use a filament dryer.

5. Prevent and undo tangles

   When loading or unloading, always hold the filament end or tuck it into the spool's holes. If it has tangled, unwind several metres, make sure no knots remain and rewind it by turning the spool. If it happens while printing, stop the print, unload the filament, undo the tangle and load it again.

   Check: The filament comes off the spool without snagging.

   If that does not fix it: If the tangle is tight, cut out the affected length and reload.

Prevention

• Seal the bag or box with desiccant as soon as you finish printing.
• Always secure the filament end on the spool.
• Store spools away from sunlight and heat sources.

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• FDM filament drying and storage guide · Elegoo
• How to Prevent and Solve Filament Tangle · Elegoo
• Sealed Box (humidity requirements for filament storage) · Bambu Lab
• Drying filament (prevention and drying methods) · Prusa Research
• Filament Pre-Printing Guide: Drying · Creality
• How to Handle Tangled or Stuck Filament · Bambu Lab