There is a common frustration in 3D printing: coming back to your printer after hours of waiting, only to find a bent, loose mess on the build plate. A print failure, especially one caused by poor first-layer sticking, can feel like a major problem. The raft is a powerful, yet often misunderstood, solution to this exact problem.
So, what is a raft in 3d printing? A raft is a throwaway, flat mesh base printed directly on the build plate, underneath your actual model. Its only purpose is to provide a stable, perfectly flat base for your print to build upon, greatly increasing the chances of first-layer success.
In this guide, we will break down the 3D printing raft. We'll explore its parts, explain exactly when you should use one, and compare it to its relatives, the brim and skirt. We will also look at its good and bad points and, most importantly, show you how to master the slicer settings for best results and easy removal.
Anatomy of a Raft
A raft is not just a simple block of plastic. It is a smartly designed structure made for a very specific job: to stick firmly to the bed and then release cleanly from your part. Understanding its parts is key to using it well.
Three Key Components
A standard raft is made of three different sections, each with an important function.
The Base Layers
These are the first few layers of the raft that make direct contact with the build plate. They are usually printed thick, slow, and with a high flow rate. Their function is to be an anchor. They create a strong, firm grip on the build surface, pushing over any small problems, leveling issues, or difficult surface textures. This strong foundation is what gives the raft its amazing sticking power.
The Interface Layers
Sitting between the thick base and your model are the interface layers. These are one or two extremely thin, delicate layers. They are the most advanced part of the raft. Their purpose is to create a controlled breaking point. They must provide just enough sticking for the model's first layer to stick to them during printing, but be weak enough that you can peel the finished model away from the raft without too much force or damage.
The Top Surface Layers
These are the final, solid layers of the raft structure. They form the clean, perfectly flat surface on which your model's actual first layer will be printed. Think of this as a brand-new, perfect build plate created just for your part. It makes sure that the important first layer of your model goes down perfectly, no matter the condition of the real print bed underneath.
When to Use a Raft
Knowing what is a raft in 3d printing is only half the battle. The real skill lies in knowing when to use it. A raft is a problem-solving tool, not a default setting. Here are the key situations where a raft is the right choice for print success.
Fighting Severe Warping
Warping is the enemy of many 3D prints. It happens when a material, especially a high-temperature one, cools and shrinks unevenly. This heat shrinking creates huge stress that can lift the corners of a print off the build plate. Materials like ABS, ASA, and Nylon are known for this. A raft fights warping by providing a massive, strongly stuck footprint. The raft itself may absorb the warping stress and lift slightly at its own edges, but it sacrifices itself to keep the actual part held down flat and secure.
Poor Bed Sticking
Sometimes, the problem isn't the material, but the build surface itself. You might be dealing with an uneven or warped build plate that your auto-leveling system can't fully fix. Or perhaps the surface material is naturally difficult for prints to stick to. In these cases, a raft acts as the great equalizer. It lays down a new, reliable foundation, effectively creating a perfect print surface where one didn't exist before.
Models with a Tiny Footprint
Consider a model that is tall and thin, or a figurine standing on its tiptoes. These prints have very small points of contact with the build plate, making them extremely unstable. A slight bump from the printhead or even vibrations can be enough to knock them over mid-print. A raft provides a wide, stable foundation that anchors these delicate models firmly in place, preventing them from detaching or tipping over.
Complex Models with Small Supports
When a model requires many small, individual support structures that start on the build plate, each one becomes a potential point of failure. If even one of these small supports detaches, it can cause a chain reaction failure across the entire print. A raft solves this by joining all the supports on a single, continuous base. This ensures every support is anchored securely, greatly reducing the risk of individual support failure.
Raft vs. Brim vs. Skirt
The terms raft, brim, and skirt are often used the same way by beginners, but they are three different tools with different purposes. Choosing the right one is important for efficiency and print quality.
The Skirt
A skirt is one or more outlines printed around the model's edge, but it never actually touches the part. Its main use is to prepare the extruder, making sure that the filament is flowing smoothly and consistently before the printer starts on the actual model. It also serves as a last-minute visual check to confirm that the bed is level. A skirt should be considered a default for almost every print.
The Brim
A brim is a single-layer-height extension of your model's first layer, attached directly to its outer edges, like the brim of a hat. Its job is to increase the surface area of the first layer, providing extra grip to hold the part down. A brim is an excellent, low-waste choice for preventing minor warping on models that have a decent, but not massive, footprint.
Head-to-Head Comparison
To clarify the choice, here is a direct comparison of the three sticking aids.
| Feature | Raft | Brim | Skirt |
|---|---|---|---|
| Primary Goal | Create a new foundation | Increase first-layer surface area | Prime the extruder |
| Bed Sticking | Excellent | Good | None |
| Warp Prevention | Excellent | Good | None |
| Material Usage | High | Low | Very Low |
| Print Time Added | Significant | Minimal | Very Minimal |
| Removal Effort | Moderate to Difficult | Easy | Not Applicable |
| Bottom Finish | Can be rough | Clean (after removal) | Unaffected |
Your Decision-Making Flowchart
Use this simple thought process to make your choice:
- Always start with a skirt. It prepares the nozzle with virtually no downside.
- If you are printing a model with a large, flat base but are concerned about slight corner lifting or sticking, add a brim.
- If you are printing with high-warp materials (like ABS or Nylon), if your model has a very small base, or if you simply cannot get your print to stick reliably, use a raft.
Raft Pros and Cons
Using a raft is a trade-off. It offers unmatched sticking but comes with costs in time, material, and post-processing.
The Advantages
- Unmatched Sticking: A raft is the single most reliable method for ensuring a print sticks to the build plate. When all else fails, a raft usually succeeds.
- Superior Warp Prevention: For materials prone to significant heat shrinking, a raft is the best defense against warping and part failure.
- A "Reset Button" for Your Bed: It effectively makes up for minor bed leveling issues, scratches, or uneven surfaces, providing a perfect first layer for your model every time.
The Disadvantages
- Increased Filament Use: Rafts are 100% throwaway material. Depending on the size of your model's footprint, this can add a noticeable amount to the filament cost of a print.
- Longer Print Times: Printing the entire raft structure before your model even begins adds significant time to the overall job.
- The Challenge of Post-Processing: Removing the raft can be a delicate operation. If settings aren't tuned correctly, it can be very difficult to separate from the model, sometimes requiring tools and risking damage to the part.
- Imperfect Bottom Surface: The surface of your print that was attached to the raft will never be as smooth and shiny as a first layer printed directly on glass or a PEI sheet. It will have a textured, matte appearance from the interface layers.
Mastering Slicer Settings
The difference between a raft that works perfectly and one that causes a headache lies in the slicer settings. While defaults are a good start, tuning these parameters is key to mastering rafts.
The Most Important Setting
The single most important parameter for raft performance is the "Separation Distance," sometimes called the "Air Gap." This setting controls the vertical distance between the top of the raft's surface and the bottom of your model.
It's a delicate balance. If the gap is too small, the model will fuse too strongly to the raft, making removal nearly impossible without breaking the part. If the gap is too large, the first layer of your model will be deposited into thin air, resulting in a messy, stringy bottom surface that didn't properly stick to the raft. A common starting point is around 0.2mm. If you find removal too difficult, try increasing this value in small increments of 0.02mm.
Other Critical Parameters
- Raft Offset: This determines how far the raft extends beyond the model's edge. A larger offset provides a more stable anchor but uses more material and time.
- Raft Layers: Your slicer will allow you to control the number of base, interface, and top layers. You might increase the base layers for a very warped bed or decrease the top layers to save a little time on a simple print.
- Raft Print Speed: The base layers of the raft should always be printed slowly to ensure maximum sticking to the build plate. Following raft layers can often be printed faster.
- Raft Fan Speed: How you use your part cooling fan can be critical. For materials like ABS, you may want the fan off for the raft's base layers to maximize sticking, but then turn it on for the interface layers to help them solidify and separate more cleanly from the model.
Pro Tips for Easy Removal
- Always start with your slicer's default raft profile for your chosen material and make small, step-by-step changes.
- Try removing the raft while the print is still warm on the build plate (but not so hot that you burn yourself). Some materials are more bendable when warm, which can make separation easier.
- Use the right tools. Don't just rip the raft off. A thin, flexible spatula, a deburring tool, or even a pair of flush cutters can be used to carefully get under an edge and gently pry the raft away.
A Professional Tool
To conclude, think of the raft as a professional tool, not a crutch. As of 2025, improvements in auto bed-leveling technology and high-performance build surfaces have reduced the everyday need for rafts, especially with forgiving materials like PLA. The main goal should always be to calibrate your printer to achieve a perfect first layer directly on the bed.
However, knowing how and when to expertly use a raft is what separates a casual user from an experienced 3D printing practitioner. It is a key that unlocks the ability to print with challenging materials, create complex shapes, and save prints that would otherwise be doomed to fail. Do not be afraid to use a raft when the situation calls for it; it is an essential part of your problem-solving toolkit.
FAQ
Q1: Do rafts use a lot of filament?
A: Yes. Compared to a brim or skirt, a raft is the most material-intensive bed sticking option. The exact amount depends on the size of your model's footprint and your specific slicer settings for raft size and density.
Q2: Will a raft ruin the bottom of my print?
A: It won't ruin it, but the finish will be different. The surface that rests on the raft will not be shiny or as smooth as a print laid directly on a glass or PEI sheet. It will have a characteristic matte, textured appearance. Fine-tuning your separation distance is the key to getting the cleanest possible surface and minimizing removal marks.
Q3: Are rafts necessary for PLA?
A: Generally, no. PLA is a very stable, low-warp material. With a well-leveled bed and a clean build surface, it should print perfectly without a raft. For PLA, a brim is usually more than enough if any extra sticking is needed for a tricky part.
Q4: Can I use a raft and supports at the same time?
A: Absolutely. Slicer software is designed for this exact scenario. The raft will print first to create a stable foundation, and then the support structures will build up from the top surface of the raft to support your model's overhangs. This is a very common and powerful technique for printing complex models.