PRUSA Spool Filament Storage ⧸ MaxFlow⁴

Your PRUSA spool deserves better than a basic silica box.

TL;DR

Everything you could want from a desiccant container for your PRUSA filament spools. Maximum airflow, secure spool retention, easy filling, a locking lid and no extra hardware required.

The locking tabs are intentionally stiff right after printing. Push the lid fully into place and insert the container into the spool core once with a little force. After that, everything moves smoothly and clicks satisfyingly into place.

It basically becomes a fidget toy that keeps your filament dry.

Designed for This Exact Spool

This is not a generic container resized to fit different spools. Every MaxFlow⁴ model is individually calculated around the exact dimensions and geometry of the specific spool it was designed for. This includes the container dimensions, wall geometry and the integrated locking tabs that engage with the spool core. The spool shown in the photos is the exact spool this version fits. If your spool looks different, please choose the matching MaxFlow⁴ version instead.

MaxFlow⁴  is also not designed to be freely scaled. The wall and mesh geometry is calculated around a 0.2 mm layer height down to the individual layer. Scaling the Z axis or slicing at a different layer height will break the intended mesh structure.

Limited X/Y scaling of approximately +/-5% is possible, but going further can prevent the slicer from maintaining the calculated wall thicknesses and extrusion paths correctly. Scaling can also affect the spool-specific locking geometry.

Maximum Airflow. Secure by Design.

Designed for maximum air exchange, secure spool retention and simple everyday handling.

The highly open woven wall structure and reinforced mesh lid and bottom expose as much of the desiccant as possible. Large open surfaces on the front, back and sides allow moisture to reach silica gel, activated alumina, molecular sieve or your preferred desiccant from virtually every direction.

Rectangular for a Reason

The rounded rectangular shape is functional from every angle.

Unlike a purely cylindrical container, the large side walls provide additional open surface area for moisture exchange instead of relying mainly on the front and rear faces.

Outside the spool, the flat sides prevent the container from rolling off your desk and make multiple containers much easier to organize and store.

More usable surface area, no rolling around, better storage. The shape earns its space.

Slide In. Click. Done.

The lid slides directly onto the container and locks securely into place with integrated locking tabs. Accidental opening during handling or spool movement is effectively prevented.

The upper rim is completely smooth and flush. No threads, no deep grooves and no awkward gaps where silica gel, activated alumina, molecular sieve or other desiccant can become trapped while filling or closing the container.

Made to Stay Where It Belongs

Inside the spool, an integrated flexible locking mechanism engages directly with the spool core and keeps the container securely in position. It cannot simply slide out when the spool is picked up, moved or handled.

The complete locking mechanism is printed directly as part of the container. No screws, springs, magnets, pins or additional hardware required.

Which Desiccant Should You Use?

Silica Gel - Keeping the Peace

For most users, silica gel is the easiest and most practical option. It is inexpensive, widely available and easy to regenerate. Around 120 °C will dry it thoroughly, but even 65 °C works if you give it enough time. It will not become completely dry at that temperature, but if you regularly dry your filament anyway, you can usually regenerate the silica together with it and skip a separate regeneration cycle.

Not sure what to buy? Stick with colorless or orange silica gel and you are on the safe side. I recommend avoiding blue silica gel, as some blue indicators may contain potentially harmful chemicals such as cobalt(II) chloride or crystal violet. 

Activated Alumina - Declaring War on Humidity

Want to take things a little further? Activated alumina typically absorbs around 20 to 30 % of its own weight in water and keeps working at lower humidity levels than silica gel. If maximum dryness is the mission, this stuff absolutely delivers.

The catch is regeneration. Activated alumina generally wants around 150 °C to 250 °C, so drying it together with your filament is usually not an option. Great performance, but be careful. Your three-day special operation against humidity might still be going according to plan five years later.

Molecular Sieve - Crimes Against Humidity

For seriously demanding moisture control, molecular sieve is the next step. It remains highly effective even below 10 % relative humidity, where conventional desiccants become less effective. The tradeoff is regeneration, typically requiring around 200 °C to 300 °C. For filament storage, 3A or 4A molecular sieves are the practical choices.

What Should You Avoid?

Skip bentonite clay if you can. It works, but it is simply too dusty to pour directly into an open desiccant container.

If all else fails, you have nothing else available and you absolutely need to use bentonite clay right now, pour it into a nylon stocking and tie it shut first. Ask your girlfriend for one. Actually, who am I kidding? Ask your mother.

And for the love of everything that is holy, never use calcium chloride. This stuff does not simply absorb moisture. It eventually turns into a concentrated salty liquid that eats electronics and metal for breakfast. Great for disposable moisture absorbers, absolutely terrible anywhere near your printer.

Filament Recommendations

Pick a filament that matches your temperature range and workflow. PETG is a great all-round choice, while ABS, ASA or PC are excellent options if the container will regularly see higher temperatures.

PLA works for short-term use, but I do not recommend it for a container that is meant to last. Over time, PLA can become brittle, especially when repeatedly exposed to elevated temperatures. Silk PLA should also be avoided due to its generally weaker mechanical properties.

If you plan to regenerate silica gel together with your filament, make sure the printed container can comfortably handle the drying temperature you use.

After printing, I recommend letting the model cool down slowly instead of removing it while it is still hot. This is especially useful with higher-temperature materials and helps the finished container retain its intended shape.