Introduction
We've all experienced this: several hours into a print, you check how it's going only to discover a tangled mess, corners peeling off the build plate, or a part that has come loose entirely. The disappointment of a 3D print failing on its first layer is something every 3D printing enthusiast knows well. Poor sticking and bending are the main problems that turn a hopeful model into a pile of wasted plastic.
This is where the 3D printing raft comes in. It is a helpful, but sometimes confusing, tool in 3D printing made specifically to solve these first-layer problems. While you don't always need one, learning when and how to use a raft can mean the difference between constant failure and reliable success. This guide is your complete resource. We will explain what a raft is, exactly when (and when not) to use one, how to set it up in your slicing software, and how it compares to other sticking helpers like brims and skirts.
Part 1: The Basics: What is a raft in 3d printing?
Explaining the Raft
A raft is a throwaway, flat mesh or grid of plastic that is printed on the build plate before your actual model starts printing. The model is then built directly on top of this raft, not on the build surface itself. After the print is finished, the raft is meant to be broken off and thrown away.
Think of it this way: you wouldn't build a tall building on unprepared ground. You first pour a perfectly flat, stable concrete foundation. The raft acts as this temporary foundation for your print. It makes sure the structure has a perfect, super-sticky base to start from, and once the building is complete, the foundation's job is done and it can be removed.
Parts of a Raft
A raft isn't just a solid block of plastic. It's a carefully designed structure, usually made of three different sections, each with a specific job.
The Base Layers
These are the first few layers of the raft that touch the build plate directly. They are usually printed with very thick lines and at a slow speed. The main goal of these layers is one thing: maximum sticking. They are designed to grip the build surface strongly, creating a solid anchor that fights against the pulling forces of warping and makes sure the entire print stays locked in place.
The Interface Layers
Sitting between the thick base layers and your model are the important interface layers. These layers are much thinner and less dense. Their purpose is two things: they create a smooth, flat surface for your model's first layer to be printed on, but they are also intentionally designed to have a weak connection with the model itself. This controlled weakness is what allows you to cleanly separate the raft from the finished part later.
The Top Surface
The very top surface of the raft effectively becomes a brand-new, perfect build plate for your model. It's perfectly level and has a consistent texture, fixing any problems from a warped, uneven, or damaged physical build plate. Your model's critical first layer is printed onto this ideal surface, making sure it starts perfectly.
Part 2: The Important Question: When Should You Use a Raft?
A raft is a problem-solver. Using one automatically is wasteful and unnecessary. You should use a raft strategically when you face specific, ongoing problems that other methods fail to fix.
Main Problems a Raft Solves
Fighting Severe Warping
Materials that shrink a lot when cooling, such as ABS, ASA, and Nylon, are well-known for warping. As the material cools, it contracts, and this force is strong enough to pull the corners of a print up and off the build plate. A raft, with its large surface area and strong sticking, absorbs these shrinking stresses. The raft may warp slightly itself, but it keeps the actual part above it flat and the right size.
Fixing Ongoing Sticking Problems
Sometimes, despite a clean bed and perfect setup, a part just won't stick. This can be due to a tricky build surface material or a plastic that is particularly hard to get a good bond with. When a print absolutely cannot be allowed to fail, a raft acts as reliable insurance, providing a high-sticking foundation that almost guarantees the print will stay put.
Stabilizing Small Contact Areas
Consider printing a small figure standing on its two small feet or any tall, thin model with a tiny base. These parts have a very small contact area with the build plate, making them extremely likely to detach or fall over during printing. A raft provides a wide, stable base far larger than the model's contact area, preventing it from being knocked over by the nozzle's movements.
Printing on Uneven Surfaces
Even with advanced automatic bed leveling, a build plate can have dips, warps, or damage from previous print removals. A raft can make up for these flaws. By laying down its own foundation, it creates a perfectly level surface a few millimeters above the flawed build plate, making sure your model's first layer is perfect regardless of the condition of the bed underneath.
A Decision-Making Checklist
Use a raft if:
- You are printing with high-warp materials like ABS, ASA, or Nylon.
- Your model has a very small surface area touching the build plate (e.g., points, small feet).
- You are printing a complex model with many small, separate "islands" on the first layer.
- Your build plate is not perfectly level or has minor physical damage.
- You have repeatedly experienced first-layer sticking failures despite troubleshooting other settings like temperature, Z-offset, and bed cleaning.
Part 3: Raft vs. Brim vs. Skirt: Choosing the Right Tool
The raft is the strongest bed sticking tool, but it's not the only one. Understanding its alternatives, the brim and the skirt, is key to using your printer efficiently.
Understanding the Alternatives
The Skirt: A Nozzle-Priming Warm-up
A skirt is an outline that is printed around the model but does not touch it. Most slicing programs enable a skirt by default. Its purpose is not sticking. Instead, it serves to prime the extruder, making sure that any old or leaked plastic is purged and that the nozzle is depositing a smooth, consistent flow of plastic before it starts on the actual model. It's a warm-up lap for your extruder.
The Brim: An Extended First Layer
A brim is a single layer of extra material printed around the base of your model, directly attached to it. It looks like the brim of a hat. Its purpose is to increase the surface area of the first layer, providing extra hold-down force. This makes it an excellent tool for fighting mild warping and improving the sticking of parts with sharp corners, without the material waste and print time of a full raft.
Side-by-Side Comparison
This table provides a quick comparison to help you decide which tool is right for your print.
| Attribute | Skirt | Brim | Raft |
|---|---|---|---|
| Purpose | Prime nozzle | Prevent warping, add sticking | Solve severe warping/sticking, stabilize |
| Sticking | None | Good | Excellent |
| Material Usage | Very Low | Low | High |
| Print Time | Minimal Increase | Small Increase | Significant Increase |
| Removal | None (not attached) | Easy (peels off) | Moderate to Difficult |
| Bottom Finish | Unaffected | Minor artifact at edge | Can be rough, imperfect |
Part 4: Mastering the Raft: A Guide to Slicer Settings
Enabling a raft is just the first step. To get a successful print that is also easy to remove, you must master a few key slicer settings.
Key Raft Parameters
Separation Distance (Air Gap)
This is the single most critical raft setting. It defines the vertical gap between the top surface of the raft and the bottom surface of your model. It's a delicate balance:
* Too Small: The model will fuse to the raft, making removal nearly impossible without damaging the part.
* Too Large: The first layer of the model won't stick well to the raft, resulting in a stringy, rough bottom surface.
A good starting point is typically equal to your layer height (e.g., 0.2mm). You should tune this in 0.02mm increments to find the sweet spot for your material and printer—where the raft peels off with a satisfying crackle, leaving a reasonably clean surface behind.
Raft Layers
This setting group defines the structure of the raft itself. You can usually control the number of thick base layers, the dense top layers, and the crucial interface layers. A typical setup might be 2-3 base layers for sticking, 1-2 interface layers for separation, and 2 top layers for a smooth surface. Reducing the number of layers can save time and material, but may hurt performance.
Raft Offset
This parameter determines how far the raft extends beyond the part's outline in the X and Y dimensions. A larger offset (e.g., 10-15mm) creates a wider, more stable foundation and provides a bigger anchor to fight warping. A smaller offset (e.g., 3-5mm) saves material and is sufficient for basic sticking improvement.
Raft Print Speed
Slicers often allow you to control the speed for different parts of the raft. For best results, the first base layer should be printed very slowly (e.g., 20-25 mm/s) to ensure a rock-solid bond with the build plate. Later raft layers can be printed faster to save time.
Part 5: The Trade-Offs: Pros and Cons of Using a Raft
Like any specialized tool, rafts come with a distinct set of advantages and disadvantages.
The Clear Advantages
- Unmatched Print Success: For difficult prints, a raft dramatically increases the probability of success, saving you from failed prints and frustration.
- Excellent Warping Solution: It is the most effective method for fighting severe warping in high-shrinkage materials.
- Stable Foundation: It provides unmatched stability for models that are tall, thin, or have a tiny contact area.
Disadvantages and How to Manage Them
While powerful, rafts are not without cost. Here are the main drawbacks and how to manage them.
Increased Time and Waste
A raft adds significant print time and can increase plastic consumption by 10-20% or more.
* How to Manage: Be strategic. Use rafts only when truly necessary. Optimize your raft settings by using the minimum number of layers and the smallest offset required to get the job done. Don't use a raft when a simple brim would work.
The Imperfect Bottom Surface
The bottom surface of a part printed on a raft will never be as smooth and glossy as one printed directly on a glass or PEI sheet. It will inherit the texture of the raft's top surface.
* How to Manage: Carefully tune your "Separation Distance" setting. A smaller gap improves the finish but makes removal harder. For a perfectly smooth finish, some post-processing, like light sanding, will almost always be necessary.
Difficult Removal Process
If settings aren't dialed in, removing a raft can be a difficult, frustrating process that can even damage the print.
* How to Manage: Tuning is everything. Adjusting the interface layers and separation distance is the key to an easy break-away. Use appropriate tools like thin spatulas, flush cutters, or deburring tools to carefully pry the raft away, starting from a corner.
Part 6: Advanced Context for 2025: Rafts in the Modern Landscape
The role of the raft has evolved. In 2025, it's less of a default requirement and more of a specialized, high-impact tool.
Rafts and Material Selection
Your choice of material is a primary factor in deciding whether to use a raft.
* Often Essential For: Engineering-grade materials like ABS, ASA, Nylon, and Polycarbonate. Their high shrinkage rates make printing large, flat objects without a raft extremely challenging.
* Sometimes Helpful For: PETG and some flexible TPUs. While PETG has low warp, it can benefit from a raft for models with very small contact areas. Flexible materials can sometimes peel up, and a raft can help lock them down.
* Rarely Needed For: PLA and PLA+. These materials have minimal shrinkage and excellent sticking properties. If you need a raft for PLA, it's often a sign of an underlying issue with your printer's setup or build surface.
Is the Raft Outdated?
Advances in 3D printing technology have significantly reduced the default need for rafts.
The Impact of Advanced Surfaces
Modern build surfaces have revolutionized bed sticking. Textured and smooth PEI sheets, G10/Garolite, and other specialized coatings provide such excellent sticking for a wide range of materials that they often make rafts, and sometimes even brims, completely unnecessary. A part printed on a clean, heated PEI sheet will stick firmly and release easily once cooled.
The Importance of Setup
In 2025, we understand that perfect printer setup is the true first line of defense. Features like automated multi-point bed leveling are now standard, ensuring a perfect first layer height across the entire bed. A precisely set Z-offset is non-negotiable. A raft should never be used as a crutch for a poorly set up machine. It is a tool for solving material-specific or geometry-specific problems that persist even on a perfectly tuned printer.
Conclusion: The Raft as a Strategic Tool
What is a raft in 3d printing? A 3D printing raft is a throwaway foundation that solves critical first-layer problems. It is an invaluable problem-solving tool, but it is not a universal first step.
The core message is simple: understand the why before you enable the what. Use a raft strategically to fight severe warping, chronic poor sticking, or to stabilize an unsteady model. For most prints in 2025, especially with PLA on a modern machine, a raft is overkill. Master your printer's setup, keep your build surface clean, and experiment with brims and slicer settings first. Reserve the raft for the tough jobs where it's truly the best tool for ensuring a successful print.
Frequently Asked Questions (FAQ)
Q1: Why is my raft so hard to remove from my print?
A: Your "Separation Distance" (also called Air Gap) is likely too small. This causes the first layer of your model to fuse too strongly to the raft. In your slicer, try increasing this value in small increments of 0.02mm until the raft separates cleanly.
Q2: Will a raft fix all my bed sticking problems?
A: It will fix most sticking-related print failures, but it can also hide underlying issues. Before resorting to a raft, always ensure your build plate is clean (washed with soap and water, then wiped with isopropyl alcohol) and that your Z-offset is correctly set for a perfect first layer "squish".
Q3: Does a raft significantly increase plastic consumption?
A: Yes. Depending on its size and thickness, a raft can easily add 10-20% or more to your total plastic usage and print time. This is a primary reason why it should be used carefully and only when necessary.
Q4: Can I use a raft with a brim at the same time?
A: This is generally not possible or necessary in most slicer software. The raft itself provides a much larger and more stable base than a brim, making the addition of a brim unnecessary. The raft's function completely replaces that of a brim.
Q5: The bottom of my print looks rough after removing the raft. How can I fix this?
A: This is the main trade-off of using a raft. To improve the finish, you can try slightly decreasing your Separation Distance, but this will make removal harder. For a perfectly smooth finish on a rafted part, a small amount of post-processing, such as light sanding, is almost always required.