Nearly all Original Prusa i3 3D printers have a spool of filament placed in the original holder on the frame. This solution is trouble-free, practical, functional and mobile. However, if you want to print from special materials, which are hygroscopic, you need to keep the filament dry also during printing – that’s what silica gel is for. We present several solutions for this case.

What is a drybox?

A drybox keeps the filament dry during printing and also protects the filament from dust. A 3D printer with our Multi-Material Upgrade not only allows you to print from filaments of different colors but also gives you the opportunity to print with different kinds of materials. A practical example: printing water-soluble supports. The usual approach is to print supports with the same filament used for printing of the model itself. Once it’s done, it is necessary to remove the supports manually – using force. This results in visible marks left on the print. In some cases, the supports may be difficult to access and may even be impossible to remove. There must be a small gap (typically 0.1 mm) between supports and the print. Therefore, the surface under the supports is not perfectly smooth. On the other hand, soluble supports can be printed without spacing and dissolved in water. The print surface is therefore much nicer.

On the picture below, you can see the different surfaces above supports. From left: without supports, with normal supports, with soluble supports.

Table of contents

  1. Drybox for one filament + four filaments without cover (for MMU2S enclosure)
  2. Dryboxes on a wall for any number of filaments
  3. Samla Drybox for three filaments (for MMU2S enclosure)
  4. 2x Samla Drybox for up to six filaments
  5. Community solutions and ideas

Drybox for one filament + four filaments without cover (for MMU2S enclosure)

When printing soluble material with the MMU2S, the soluble filament should be in the fifth filament slot (as default). That is why the drybox is adapted to the location on the right. The modular filament holder is a part of the construction of the MMU2S Printer Enclosure V2. We created an alternative part that works as a cover / drybox for the fifth filament.

Benefits of our drybox

  • filament is protected from dust
  • filament is in a dry environment thanks to silica gel
  • simple and functional oval filament outlet which is covered by a piece of foil
  • easy to load filament
  • easy replacement of silica gel thanks to the tray on the bottom of the box

Parts and fasteners

  • printed plastic parts (preferably PLA material) – make sure you chose the right parts depending on whether you want to place the humidity sensor in the box or not
  • 2x M3x30 screw
  • 3x M3x10 screw
  • 1x M3x5 screw
  • 4pcs of 608RS bearings (from original spool holders)
  • 2pcs aluminum tube diameter 7.8 mm (from original spool holders)
  • plastic film from Prusament coil (or similar quality film 0.1mm thick
  • humidity sensor – optional
  • silica gel

Building the box

  1. Shorten the aluminum tubes from the original spool holders to 100 mm length.
  2. Secure the box closing knob with the M3x10 screw. Make sure that the pin on the bottom of the box fits into the groove in the knob.
  3. Cut the same size foil from a Prusament bag so it fits the frame.
  4. Insert the foil and frame into the box and secure them from outside with two M3x10 screws.
  5. Use a sharp scalpel to cut the foil in the middle of the groove.
  6. Screw the M3x5 screw into the lid.
  7. Attach both halves together with two M3x30 screws.
  8. Place the tray on the bottom of the box and fill it with silica gel.
  9. Place bearings on the axes and snap them into the box.
  10. Push the humidity sensor into the box.

During testing, the air humidity was kept below 20% in the box at an ambient air humidity of approximately 45%.


Dryboxes on a wall (for any number of filaments)

This drybox is of a similar design as the first one. However, this version can be secured onto a wall. You can use any number of dryboxes. When used with the MMU2S, it is recommended to attach the filament buffer under the dryboxes onto the wall, but you can also try printing without the filament buffer. If you do not have a multimaterial upgrade, you can use multiple boxes as storage space and have several materials at hand, so they can be switched quickly and easily.

The assembly of these dryboxes is similar to the previously described design. This versions, however, have the filament outlet at a different location and it also has mounting holes. Use these buffer mounts when mounting the buffer onto a wall. Be sure to select the right model to print depending on whether you want to use the humidity sensor. We recommend using PLA for printing – we used Prusament PLA Prusa Galaxy Black.

Samla Drybox for three filaments for MMU2S box

A slightly less refined design, yet a very simple and functional solution is a drybox built made using Ikea Samla boxes. The box can easily fit two filaments. If you print the middle holder, the third filament will also fit inside.

Material for the 3-filament version

  • printed plastic parts of sliders and middle filament holder
  • filament buffer holders
  • printed lid clips
  • 1x IKEA Samla box with lid 39x28x28 cm / 22l
  • 12x 608RS bearings (from original spool holders)
  • 4x 7.8 mm aluminum tubes (from original spool holders)
  • 2x original spool holder
  • 6x M3x18 screw
  • 4x M3x10 screw
  • 10x M3 nuts
  • 4x 3,5×20 wood screw or similar (mounting box to the table)
  • 2x 3,5×35 wood screw (filament buffer mounting)
  • humidity sensor – optional
  • silica gel

Assembly instructions

  1. Place the slider on the box and mark the holes on the box where the sliders will be attached with screws.
  2. Drill the holes in the indicated locations with a 4 mm drill bit.
  3. Place the inner slider part on the box and align the part with the drilled holes.
  4. Mark the oval holes in the box slider with a marker.
  5. Create oval holes by drilling a hole next to hole with 5mm diameter drill bit and then cutting the residue with a sharp knife. ATTENTION – the box material is fragile.
  6. Attach the sliders onto the box (M3x18 screws).
  7. Unscrew the filament buffer and replace the middle holders with new ones.
  8. Place the drybox in the center of the top lid and screw it with four screws. We recommend pre-drilling holes in the box.
  9. PTFE tubes should be approx. 0.5 cm from the drybox.
  10. Place the two original spool holders in the box and fill them with silica gel.
  11. Place the humidity sensor inside the box.
  12. Assemble the printed middle filament holder and place it in the center of the box.
  13. Pass the filaments through the sliders and secure the lid with the printed clips

During testing, the air humidity was kept below 20% in the box at an ambient air humidity of approximately 45%.

2x Samla Drybox for up to six filaments

The Samla Drybox design can be used without Prusa Printer Enclosure V2 – the printer with the MMU2S upgrade can be placed on a table (see the picture below). In such a case, it is even possible to place two boxes on top of each other. Then there is enough place up to six filaments. According to our tests, this solution can be used without a filament buffer. Place the boxes behind the printer so that the PTFE tubes from the MMU2S unit end close to the drybox sliders. Building material is identical to the previous solution, only the amount of material used is doubled.

Silica gel can be re-dried in an oven and then reused.

Community solutions and ideas

Original Prusa printer owners are usually very creative people and true makers, who often design and produce their own printer accessories. At, there’s plenty of various add-ons, tweaks, and mods. However, keep in mind that not every “upgrade” brings only benefits. Non-original filament setup can, in some cases, negatively affect print quality and reliability. Always assemble and test your 3D printer as stated in original instructions, before you start to experiment with mods.

Do you have your own original solution you would like to show? Share your models and prints on, on our forumTwitterInstagram or Pinterest and we will add them to the gallery below.

Happy printing!