The Official


Filament Buffer

Side Feed Option Top Feed Option Bear Frame Option Compact Reliable Robust Professional Functional

Design Brief

The Wedge RMU Mk3 - What is it?

The RMU (Retraction Management Unit) expands the flexibility of the Prusa MMU by giving the following benefits.
• It works! You don’t have to troubleshoot it. Fit it to your printer and thats it.
•The RMU is a Tower Buffer. It stores filament in the body section of the tower when not in use 

A compact storage for material not in use, the 5 channel RMU fits snugly to the rear of the Prusa I3 Mk2 & Mk3 and Bear Frame.

• Form meets function, the beautiful minimalist design looks perfect and does not impede the printer in any way.
• No messy tangles of filament as it winds back between material changes.
• Almost frictionless feeding of material. Does not strain to the feeder mechanism.
• Simple, reliable loading of material into the buffer. You can even do it on the fly.
• The RMU expands the footprint of the Mk3 by just 40mm on the left side of the printer.
• Short travel distance between RMU and MMU.
• Utilises existing Prusa mount points
• Safe parking of material at jobs end
• Easy side load of filament
• Opening the buffer still keeps all the material constrained – no messy loops of material
• Super easy access to load and unload filament.


Product Range

BF001: Completed printed buffer

We offer to produce and supply the complete RMU-Mk3. The total print time is nearly three days which some people may find onerous. The complete kit comes supplied with all the fittings pre-assembled so all you have to do is attach the top, base and the brackets and Teflon tubes. You can choose which version you would like, Mod-S or Mod-T with Mk3 or Bear frame Chassis

Mod-S is pictured which support feeding from the left or underneath the printer.

Mod-T allows for feeding from above, or right side of the printer. 


We have designed custom mountings for the Bear Frame and the original Prusa Mk3 Chassis.

You will receive all the component parts of the RMU-Mk3 plus a bill of materials, links to assembly instructions, tips and tricks and any other resources we think you might find useful.


BF002: Hardware Package & Files

Our most popular option is to provide all the fittings. We will email the print files so you can print the RMU-Mk3 yourself. Print time is around three days in total so we aim to get the fittings to you as quickly as possible. The STL files include the option to make either the Mod-S or Mod-T variations.

You will receive all the fittings to assemble the RMU-Mk3 plus a bill of materials, a download link for the STL files, links to assembly instructions, tips and tricks and any other resources we think you might find useful. 

All fittings are posted, files are emailed,


BF003: Online package - Files only

Power users may prefer to source the fittings themselves. This lowest cost option allows you to print the RMU-Mk3 yourself and supply and fit your own fittings. Most items are commercially available but it can be costly to do this your self so we will always recommend buying the BF002 option. the STL files include the option to print the Mod-S or Mod-T variations.

You will receive via a download link, the print files plus a bill of materials, links to assembly instructions, tips and tricks and any other resources we think you might find useful. 

Files and BOM are provided via a download link.

3D schematic filament buffer


We recommend the RMU-Mk3 is manufactured in PETG for the best results.

PETG gives good mechanical properties, strength, durability, low shrinkage and close tolerances.

We print our complete products in Prusament PETG, Orange or Black to match the printer.



In operation, the RMU provides peace of mind through multiple material changes when producing parts in multiple colours or material types. 

The filament buffer allows for the ejected material to be fed back easily for storage between use.

The very short distance between the MMU and RMU filament buffer means that loading new material is easy. 

Because the RMU filament buffer is so easy to load, it makes using the Prusa MMU simple. Simply feed filament into the RMU, pop the top open, feed to the MMU and you’re ready to print.


Other Printers

We have designed the RMU Print Buffer to fit all of the Prusa Mk3 printers. However, we will be releasing updates to include other printers where the MMU can be made to fit.


The answer is NO. Its a 3D printer and the tubes are in a much less tight 3D turn to the MMU than they appear.


We don’t think so. You don’t have to look far to see there are dozens of attempts to create a filament buffer that fits the bill of our design brief. this is the first to meet all of those demands.


We looked at the range of filament buffers other people had made and thought we could do it better. We are sure there are plenty of functional filament buffers around but none of them combine all of these features; ease of use, accessibility, compactness, robustness.

No! in fact, thats the entire purpose of the RMU. We have not had one single tangle or jam of filament in thousands of hours of printing.

The Filament Buffer is the result of hundreds of hours of design and hundreds more of testing. We have designed a mature product that will complement your Prusa MMU2S. You don’t have to troubleshoot it yourself, just fit it to your printer and it works.