An Evolution of Innovation: Prusa S Models

Prusa Research has a history of iterative innovation, focusing on refining its core product, the i3, over more than a decade. The Original Prusa MK4S, represents the culmination of years of development and customer feedback. This continuity in design philosophy means users can invest in a Prusa printer without worrying about obsolescence. The company offers upgrade kits to allow existing owners to enhance their machines without discarding them. If an early Prusa customer was so inclined, one could have found an upgrade path from the Original i3 MK1 to the MK4S.

Historically, the “S” model upgrades for both the MK2S and MK3S focused on improving reliability, durability, and ease of maintenance. Key enhancements included more robust mechanical components, better filament handling, and improved access to critical parts like the hotend and extruder for smoother, more consistent printing. The MK4S is no different with a batch of upgrades that translate into improved print quality, faster print speed, and quality of life improvements. On paper, the bed-slinging MK4S is on par with the total print times of popular Core-XY printers touted for such high print speeds.

Let’s break down the new additions offered by the MK4S:

High-Flow Nozzle

The Prusa MK4S comes equipped with a custom-designed, high-flow Core Heating Technology (CHT) nozzle that features a special core that separates the filament into three discrete channels. Such a nozzle ensures that the filament is not only melted from the outside in, but also from the inside out enabling higher melt rates which not only boosts printing speed but also enhances the durability of printed models. An additional benefit is that users can achieve impressive performance with their favorite, familiar filaments as opposed to switching to specialized high-flow filament variants. Users can expect a 50% to >100% improvement in flow rate (depending on the material and nozzle diameter) when compared to the flow rate of the standard MK4 nozzle. For those interested in even greater versatility, Prusa offers an optional Nextruder nozzle adapter, allowing users to install any V6-compatible nozzle with ease.

360° Cooling System

The most conspicuous change to the MK4S is that big ‘ol fan. The previous side-mounted fan has been replaced by a front-mounted turbine set at a 45° angle. Combined with the 360° shroud, the nozzle is uniformly enveloped in cooling air enhancing print quality, particularly in challenging overhangs at angles up to 75°! Reducing support usage translates into both less material wasted and less time printing the part. Impressively, this fan manages to operate with minimal noise. Unlike many of its high-speed competitors, the MK4S maintains a noise level that won’t disrupt an office environment making the MK4S suitable for shared workspaces where quieter operation is appreciated.

Enhanced Connectivity and the Prusa Mobile App

The MK4S is designed to function seamlessly in an offline mode, allowing users the option to avoid network use without any compromise in functionality. It can be fully set up and operated without internet access. The Wi-Fi module is also easily detachable and may be removed to meet stringent safety protocols. For those who prefer network integration, the Original Prusa MK4S includes both built-in Wi-Fi and an Ethernet port, enabling full control through the Prusa Connect system. Prusa Connect allows users to kick off prints from a browser, schedule print jobs, and remotely monitor the printer via a connected webcam. The optional Prusa app further simplifies Wi-Fi setup with a convenient NFC tap for quick and hassle-free configuration thanks to the new NFC antenna.

Expandable Features and Customization

Prusa Research’s dedication to meeting user expectations extends to offering modular enhancements. The MK4S 32-bit xBuddy electronics are built to accommodate additional add-on accessories for the ultimate customization. A GPIO module enables peripherals such as lights, camera triggers, or servos to be operated via gcode, appealing to enthusiasts who love to tweak and personalize their setups. For users that make extensive modifications to the extruder/hotend assembly, the accelerometer module can easily measure the resonance frequency of each axis and recalibrate the modded MK4S Input Shaper to the optimal values, ensuring your modded 3D printer operates with maximum efficiency. Neither of these optional accessories was evaluated as part of this review; however, they are available for purchase and are compatible with all Prusa printers utilizing the xBuddy electronics.

Printer Unboxing and Assembly

I received a fully assembled MK4S for review which retails for $1,099 at the time of writing. It is also offered as a DIY kit for $799 as well as an upgrade from the MK4 for only $99. The printer was securely packaged in custom-cut foam and cardboard as have all Prusa models back to the Prusa MK2. The Original Prusa MK4S retains the familiar aesthetic of the i3 series, with its recognizable orange and black color scheme. The screen housing is injection-molded while PC Blend Carbon Fiber is used for some of the toolhead printed parts, enhancing their strength and heat resistance. The package also included the following: a toolset (including lubricant for the bearings, alcohol-saturated wipe, and acupuncture needle), a smooth PEI print sheet, a spool holder, a 3D printing handbook, and a 1-kg spool of Prusament PLA Prusa Galaxy Black. No true assembly was required other than mounting the spool holder to the top of the printer frame.

After the initial power-up, I opted to use the optional Prusa app integration which was a breeze due to the built-in NFC antenna which could receive my Wi-Fi credentials directly from my phone. The MK4S then performed a series of self-tests evaluating the X/Y/Z axes, the hotend and bed heating elements, the cooling fans, and the filament loadcell sensor. Ultimately, I was printing within 5 to 10 minutes after flipping on the power switch.

In Use

Each print started with a quick check of the X/Y axes, a nozzle cleaning process, and a bed mesh leveling which only covers the bed area containing the print. The supplied USB drive contained a set of pre-sliced files for PLA that emphasized the advantages of the Prusa MK4S. There was an 8-minute “bonkers” Benchy, the infamous rocket engine MK4, a fidget toy, and an overhang stress test reaching 75° just to name a few. I loaded the supplied Prusament PLA and worked my way through the sample files. The prints all maintained good adhesion to the print surface while exhibiting exceptional surface finish. I loved how bridging occurred with ease, and those 75° overhangs just floated in midair.

Setting up PrusaSlicer was a smooth process due to the setup wizard which allows the user to configure which printers and filament one would like to access while slicing. I later verified that the supplied pre-sliced files could be replicated in PrusaSlicer using the default Prusa MK4S printer profiles except for the “bonkers” Benchy.

I sliced the objects in PLA for comparison on a standard MK4 where I used the “0.20mm SPEED” profile for each respective printer, and I sliced the objects in both PETG and ASA for comparison with the PLA results. Since I set up the printer with remote access via the Prusa App, I was able to send all of my sliced objects directly to the printer using Prusa Connect. This functionality is not required to use the MK4S as I could have sliced the files directly to the provided USB drive. Users who embrace these remote connectivity features via ethernet or Wi-Fi gain access to scheduling prints and remote monitoring functionality. I really enjoyed the ability to queue/schedule prints from Prusa Connect while the MK4S was printing or even send gcode files from Printables via my phone. Octoprint and Mainsail users will notice that Prusa Connect is not as feature-rich as they are used to, but it just works well for the given task of remote printer monitoring and print job scheduling.

I then moved on to two different types of printing workflow to compare use cases for routine printing: functional work-related parts and toys for the annual Toys For Tots toy drive. Ultimately, the MK4S just plowed through my printing workload with ease. Prusament filament was meant for printing at these higher flow rates, and I worked my way through various other filament brands feeling equally impressed.

I had a challenging time identifying which printer produced the PLA parts at first. To my surprise, there were subtle advantages to the exterior finish, bridging, and overhangs for the MK4S. Although the part cooling is better on the MK4S, this comparison also emphasizes how good the original MK4 part cooling is. The time savings ranged from 5% to 15% faster prints across the resliced, Prusa-provided objects as well as my non-Prusa-provided test prints. Functional work-related parts could be cranked out on draft settings at volumetric flow rates of 28–30mm3 allowing multiple rapid prototyping iterations within the workday. The Toys for Tots prints were only discernible as to printer origin because I wrote the information at the bottom of the print.

As I pushed the higher speeds to filaments other than PLA, it was obvious that high-temperature materials need to be printed in an enclosure. PETG parts were stunning; however, larger prints exhibited some delamination from both the textured and satin bed sheets. I found that baby-stepping 0.1mm–0.15mm lower on the textured or satin bed sheets improved this result. Smaller ABS and ASA parts could be printed without an enclosure (if you could tolerate the odor which I do not recommend), but larger prints need to be performed in an enclosure to ensure successful bed adhesion.

Was it a perfect experience? Almost! The only issue I ran into was with the load cell warning me of stuck filament. After my first few PLA prints, I received warnings that the stuck filament had been detected. This warning paused the print and requested that I remove and reload the filament. Despite this warning, there was nothing wrong with the print, so I refer to this as a false alarm. After disabling this feature, I never received the warning again nor did my printed parts appear to have a clogged nozzle.

Conclusion

The Prusa MK4S is a fantastic balance of part cooling and high-flow rate printing with the promise of continued software and firmware updates into the future. The CHT nozzle is the real enabler for pushing these faster speeds and is complemented by the robust cooling system for achieving that gorgeous surface finish and supportless printing up to 75° overhangs. This is the one-two combo that Prusa i3 fans have been waiting for over the past few years while competitor Core-XY printers were stealing the limelight. Even better, users can achieve this performance with their favorite filaments as opposed to seeking out high-flow capable variants. The Prusa app, Prusa Connect, and NFC setup are welcome quality-of-life upgrades, and I look forward to playing with the optional accelerometer and GPIO modules.

I did not have a perfect experience with the “stuck filament detection” false alarms and tweaked nozzle height baby-stepping, but I anticipate that future firmware improvements will rectify these nit-picky shortcomings. These faster speeds also amplify the need for an enclosure when printing ASA and other high-temp filaments. Base pricing for both the assembled and kit versions is more expensive than the competition considering both bed-slinger and Core-XY; however, the MK4 to MK4S upgrade for $99 is a bargain. The Original Prusa MK4S represents the culmination of years of development and customer feedback. This continuity in design philosophy means users can invest in a Prusa printer without worrying about obsolescence.