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Storing filament: box, vacuum bag and desiccant

Filaments6 min readUpdated: 10/2026

are explained briefly when you hover over or tap them.

The short answer: filament should be stored airtight with desiccant, ideally with a small hygrometer in the box. Bambu Lab recommends a humidity below 20 % for most filaments. Whether you use a box with a seal or a vacuum bag is secondary. What matters is that as little damp room air as possible reaches the spool.

Why this matters: almost all filaments absorb moisture from the air. Damp filament crackles, strings and prints rough, brittle parts. How to get it dry again is covered in Drying filament.

How quickly does filament get damp?

Bambu Lab gives concrete figures in its own wiki:

  • Normal room air usually has 45 to 65 % relative humidity, more in damp weather.
  • At around 55 % room humidity, freshly dried filament absorbs enough moisture again within 2 to 12 hours for print quality to suffer noticeably.
  • In an environment with 20 %, filament stays dry for about 2 to 7 days, depending on how strongly the material absorbs water.

The lower the humidity, the longer the filament stays dry. According to Bambu Lab, nylon types such as PA, PA-CF and PA12-CF are particularly sensitive. TPU, PC and PVA are also among the materials that absorb water quickly, see the table in Drying filament.

The four building blocks

1. An airtight container

Bambu Lab recommends an airtight box, and its wiki gives 4 litres as the size. What matters:

  • A seal all the way round the lid. A simple click lid keeps dust out, but not humidity. This applies to boxes from DIY stores just as much as to boxes from furniture stores such as IKEA. Before buying, check whether the lid has a rubber or silicone seal.
  • Preferably one box per spool or per material. Every time you open it, damp air gets in. Prusa writes of its own drybox that it can take up to an hour after closing for the humidity to drop again.
  • Check the seal. Prusa recommends taking a quick look at the seal every time you open the box, because a badly seated seal lets the humidity rise.

For larger collections there are also big boxes for several spools. In that case it is especially worth keeping sensitive materials such as nylon separate, so they are not opened every time.

2. Desiccant

Desiccant binds the water from the air in the box. The common types:

DesiccantProperties according to Bambu Lab
Silica gel with colour indicatorBeads change colour when saturated (with Bambu from yellow or orange to purple). Can be dried and reused.
Molecular sieveLowers the humidity at room temperature faster and further than silica gel and stays effective at higher temperatures too.
Calcium chlorideBecomes liquid when saturated. Bambu Lab no longer uses it in new AMS units because of the risk of leaking and corrosion.

Bambu Lab advises “enough effective desiccant” in the box, and checking it regularly and replacing it when it no longer works.

3. A hygrometer

A small digital thermo-hygrometer shows you whether the box is still dry. Bambu Lab explicitly recommends this for sensitive materials and gives a target value below 20 %. If the reading rises even though the box is closed, the desiccant is saturated or the seal is leaking.

4. Discipline

  • Put the spool back in the box after printing; do not leave it hanging in the printer for days.
  • Secure the end of the filament, for example in the holes at the edge of the spool. Bambu Lab points out that this stops the winding from loosening and tangling later.
  • With very sensitive materials, print straight from the box or from a dryer. Prusa’s drybox and Bambu Lab’s wiki describe exactly this set-up: the filament runs through an opening or a tube from the closed box to the printer.

Why vacuum bags?

Many manufacturers supply spools vacuum-packed with a desiccant sachet. Polymaker describes it like this: the filament is dried before shipping and then vacuum-sealed together with desiccant so that it arrives dry at the customer.

For storage at home, the vacuum bag has two advantages:

  • Little air, little water. The less air in the bag, the less moisture can reach the spool in the first place, and the less the desiccant has to bind.
  • Space-saving. Bags can be stacked and need less room than boxes.

Drawbacks: the bag has to be opened and resealed for every print, and a small hole makes it useless without you noticing. A hygrometer hardly fits inside. For spools you use often, a box with a seal is more convenient; for stock and rarely used colours, the vacuum bag is practical.

A dry box is not a dryer

A passive dry box (drybox) keeps dry filament dry. It does not make damp filament dry again. Prusa states this explicitly for its own drybox: filament that is already damp has to be dried beforehand.

If you are looking for the “best dry box”, distinguish between:

DeviceWhat it can do
Passive box with seal and desiccantStoring and printing from a dry environment
Filament dryer with heatingDrying damp filament, and with many models also during printing
Multi-colour system with dryingDepending on the model, storing, printing and drying in one device

What to look for when buying a dryer is covered in Buying a filament dryer. Maximum temperature, number of spools and prices of current devices are shown in the filament dryer comparison.

Drying desiccant again

Saturated silica gel can be regenerated. For its silica gel, Bambu Lab describes the following:

  1. Spread the beads flat on a heat-resistant surface, not in the plastic casing.
  2. In the oven at 80 to 90 °C, at most 100 °C, otherwise the structure is damaged.
  3. Slightly discoloured: 1 to 2 hours; fully saturated: 2 to 3 hours.
  4. Let it cool and pack it airtight immediately if it is not going straight back into the box.

According to Bambu Lab, the desiccant can be reused 5 to 15 times. If the colour only changes slowly or the beads crumble, it is spent. Bambu Lab also recommends not using the same tray you use for food. Other desiccants have other limits; here the information on the packaging applies.

Further notes

  • Cool, dry, dark. In its data sheets, Extrudr specifies room temperature (18 to 27 °C), dry storage and no direct sun or heat. With correct storage, Extrudr gives a shelf life of 2 years.
  • Cardboard spools and dryers. Polymaker writes that cardboard spools tolerate higher temperatures when drying than plastic spools, which can warp. In multi-colour systems with drive rollers at the edge of the spool, cardboard spools can slip or produce paper dust, according to Polymaker. Polymaker recommends printed adapter rings for this.
  • Keep an eye on the remaining amount. You can work out how much filament is left on a started spool from its weight with the filament calculator.

In short

QuestionAnswer
How dry?below 20 % relative humidity (Bambu Lab)
With what?airtight box with seal or vacuum bag, plus desiccant
How to monitor?hygrometer in the box, colour change of the desiccant
Regenerate desiccant?silica gel at 80 to 90 °C, at most 100 °C (Bambu Lab)
Does a dry box dry?No, it only keeps things dry. Dry damp filament first.

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