The Prusa i3 MK3 and MK3S are two highly capable desktop 3D printers, but distinguishing between them reveals critical design improvements. When deciding between the Prusa i3 MK3 and the MK3S, the primary distinction is the filament sensor technology and the resulting extruder redesign. This article evaluates the extruder modifications, filament sensor variations, minor hardware revisions, supported printing materials, and the specifications of these machines. You can compare 3D printers using a structured approach, but evaluating these specific revisions will help you understand the evolutionary steps of the Prusa i3 series.
What is the difference between Prusa i3 MK3 and MK3S?
The main difference between the Prusa i3 MK3 and MK3S is the filament sensor mechanism and the associated extruder assembly. Prusa Research updated the optical filament sensor to address reliability issues caused by certain filament colors and transparencies. This change necessitated a complete redesign of the extruder body. Both printers maintain the same build volume of 250 x 210 x 200 mm and operate on similar firmware. According to the Prusa3D forum documentation, from a technical standpoint, the filament sensor type is the only major difference. It dictates the need for different firmware versions to accommodate the different sensor hardware.
Extruder and Print Quality Differences
The extruder redesign on the MK3S provides better thermal management and part accessibility. By adjusting the layout, the motor extruder and nozzle are mounted closer to the X-axis carriage. This proximity reduces resonance during rapid movements. It improves overall print quality by minimizing vibrations. The MK3 uses an older extruder body design that requires more disassembly for maintenance. The MK3S alters the fan shroud geometry and the mounting method for the Noctua cooling fan. These printed part modifications simplify the process of swapping the PTFE tube or the nozzle.
Both extruders utilize Bondtech dual gears to grip the filament securely from both sides. They share the same E3D V6 hotend assembly. According to community discussions, the all-metal parts of the hotend, including the thermistor and heater cartridge, remain identical between the two versions. The printed parts of the extruder are different to accommodate the revised filament sensor hardware.
Filament Sensor Technologies
The filament sensor dictates how the printer detects filament runout and loading. The Prusa i3 MK3 utilizes an indirect optical sensor that reads the movement of the filament. According to Prusa’s documentation, this optical system struggles with translucent filaments and specific colors. It leads to false runout triggers. The MK3S implements a mechanical lever system paired with an infrared (IR) sensor and a magnetic assist. When filament enters the extruder, it pushes a small steel ball that actuates the lever. The lever then breaks the IR sensor beam. This setup is virtually immune to the optical properties of the filament. It provides reliable detection across all material types.
The transition to this lever-based IR sensor means the printer no longer relies on reflecting light off the filament surface. It physically detects the presence of the filament. This improves the reliability of the auto-loading feature and prevents failed prints caused by incorrect runout detections.
Hardware and Mounting Revisions
Several minor hardware revisions separate the two models. The MK3S introduces new belt tensioning methods on the X and Y axes, making calibration more precise. Motor mounts and the extruder cable management bundle received structural updates to prevent wire fatigue. The MK3S also modifies the Y-axis bearing clips, moving away from U-bolts to printed clamps for even pressure distribution on the linear bearings.
Despite these changes, the fundamental motion system remains identical. Both machines utilize the EINSY RAMBo motherboard paired with Trinamic 2130 drivers. Electromaker reports that these drivers offer 256 microstepping for ultra-quiet operation and enable sensorless homing for the X and Y axes. Both printers also feature power loss recovery and detection, allowing them to resume printing after a power outage. They use the P.I.N.D.A. 2 probe with a thermistor for fast temperature calibration and automatic mesh bed leveling.
Supported Printing Materials
Both the Prusa i3 MK3 and MK3S support a wide array of printing materials, including PLA, ABS, PET, TPU (Flex), HIPS, Nylon, ASA, Bamboofill, Bronzefill, and T-Glass. They share the same E3D V6 all-metal hotend. It reaches a maximum nozzle temperature of 300°C. The magnetic heatbed with a removable PEI spring steel sheet heats up to 120°C. It provides excellent adhesion for engineering-grade plastics. The heatbed also features cold corners compensation for a warpless 3D printing experience.
While Resin vs Filament 3D Printing determines the foundational technology of your project, both of these FDM machines are equipped to handle abrasive carbon-fiber filled filaments and polycarbonates if fitted with a hardened steel nozzle.
Prusa i3 MK3 vs MK3S Specifications Comparison
The core specifications of both printers remain largely unchanged. The table below outlines the primary metrics based on manufacturer-listed specifications published by MatterManifest and Electromaker.
| Specification | Prusa i3 MK3 | Prusa i3 MK3S |
|---|---|---|
| Build Volume | 250 x 210 x 200 mm | 250 x 210 x 200 mm |
| Max Nozzle Temperature | 300°C | 300°C |
| Max Bed Temperature | 120°C | 120°C |
| Hotend | E3D V6 | E3D V6 |
| Extruder Drive | Bondtech Dual Gears | Bondtech Dual Gears |
| Filament Sensor | Indirect Optical | Mechanical Lever with IR Sensor |
| Motherboard | EINSY RAMBo (Trinamic 2130) | EINSY RAMBo (Trinamic 2130) |
| Max Travel Speed | 200 mm/s | 200 mm/s |
Both printers originally launched with DIY kit and pre-assembled options. The Original Prusa i3 MK3S retailed for $750 as a self-assembly kit, or $1,000 for the fully assembled and tested unit.
Is the Prusa i3 MK3S worth the upgrade?
Upgrading from the MK3 to the MK3S provides a tangible benefit in daily reliability, specifically regarding filament loading and runout detection. The mechanical lever IR sensor eliminates the false readings associated with the older optical sensor. The redesigned extruder also makes routine maintenance, such as clearing a clogged PTFE tube, significantly faster. The core print quality remains comparable. The upgrade is primarily a quality-of-life improvement rather than a generational leap in performance. For users who frequently experience filament runout issues with specific colors or transparent materials on the MK3, the MK3S extruder upgrade provides a definitive solution.
What are the differences between MK3S and MK3S+?
The Prusa i3 MK3S+ is a refinement of the MK3S, focusing on the bed leveling probe and bearing mounts. The MK3S+ replaces the PINDA V2 probe with the SuperPINDA. The SuperPINDA is temperature-independent. It eliminates the need for a thermistor and ensures consistent first layers regardless of ambient heat. The MK3S+ also includes metal clips for the Y-axis bearings instead of U-bolts. It makes assembly easier and prevents bearing deformation.
How do you upgrade from MK3 to MK3S?
Prusa provides an official upgrade kit to transition an MK3 to an MK3S or MK3S+. The process requires completely rebuilding the extruder assembly. The upgrade kit includes the new IR filament sensor, the connection cable, a steel ball bearing, magnets, and a replacement PTFE tube. You must also print the new extruder housing and fan shroud parts before disassembling the printer. If you are taking the extruder apart to fix a clog, you are already completing a significant portion of the upgrade labor. Reviewing other 3D printer versus guides can provide context on how manufacturers handle hardware iteration cycles.