The first layer is what most people consider the beginning of a print, but it’s not always the first thing printed on the build plate. Most of the time, your slicer profile will have an adhesion assistant activated that is printed before the first layer in a print.
These adhesion assistants are meant to achieve two main tasks. The first is to check that your printer’s extrusion is working properly by laying out some filament before starting on your print. The second purpose is, in most cases, to help the first layer stay attached to the build plate throughout the print.
Adhesion assistants come in three forms: skirt, brim, and raft. Each is different in its structure and usefulness. In this article, we’ll go over each one, discussing what it is, when to use it, some advantages and disadvantages, relevant slicer settings, and more.
We’ll look into the main settings for skirts, brims, and rafts that can be modified in the latest stable version of UltiMaker Cura (version 5). We’ve opted for Cura because it’s the most popular 3D slicer program. Plus, its adhesion assistant settings are similar to those of other 3D slicers.
In our first section, we’ll go over the skirt form of adhesion assistant. While a skirt doesn’t directly help adhere a model to the build plate, it primes the nozzle before a print and indicates how level the bed is. In the sections below, we’ll discuss more about skirts and how they are helpful!
A skirt is the least intensive type of adhesion assistant when it comes to added print time, material consumption, and first layer adhesion. A skirt takes the form of a small perimeter that surrounds the area of a print but doesn’t connect to it or touch the first layer at all. It can be a few nozzle-passes wide (multiple lines), but it’s always only one layer in height.
Although we typically refer to a skirt as a type of adhesion assistant, it doesn’t actually provide adherence for the first layer like the other forms of adhesion assistants. Since it’s not directly attached to the first layer, it doesn’t expand the model’s surface area on the build plate. Therefore, it doesn’t improve the model’s print bed adherence.
Skirts, however, can tell you that your printer’s extrusion is working properly and are also a great tool to check whether your printer’s bed is level. Moreover, seeing the skirt come out okay will indicate that your nozzle isn’t clogged and that your printing area is pretty even.
As skirts are more indicators of the printer’s readiness, we suggest using them for prints where you don’t expect bed adhesion to be a problem. This includes models with a large surface area resting on the print surface because these aren’t as likely to warp or have other adhesion issues.
You should also consider using a skirt when you’re concerned about material consumption and print time. A bad skirt will quickly indicate with very little material there’s a larger problem that may lead to print failure.
Of course, if you don’t need to be reassured that your printer’s extrusion is running smoothly and that your bed is level, you may not even need a skirt. However, it’s generally recommended that you always use a skirt (when you’re not using a brim or a raft) because it costs almost no time or material and can be quite beneficial.
As we indicated, adhesion assistants can be activated and adjusted in the 3D slicer, and there are a few related settings that control how a skirt is printed.
The second form of adhesion assistant is the brim. Brims lie in the middle of the three adhesion assistants, offering more bed adhesion than skirts but not as much as rafts. As with skirts, in addition to information about brims, we’ll go over the pros and cons, and the best settings in Cura.
Brims are very similar to skirts in that they’re multi-line structures that are always only one layer in height and form a perimeter around the first layer of a printed model. However, unlike skirts, a brim is always directly connected to the first layer. This means that a brim actually expands the surface area that’s in contact with the print bed, helping keep a print adhered.
On top of helping with adhesion, brims accomplish the same things as a skirt, too: They allow you to check that your printer is extruding filament properly and that the bed is level in the areas where your print will occur.
While you can adjust the number of nozzle passes (lines), the width of the brim is typically larger than that of a skirt. This means that most brims increase a print’s material consumption compared to a skirt, but note that they still use less filament than a raft. The same is true for print time.
It’s important to note that, because brims connect to a model, you’ll have to remove them after a print is finished. While you can simply tug on the brim and tear it off, this usually doesn’t remove it all, and you might have to carefully cut it off the first layer of your print with a small blade. Even when you do this, though, the brim may still have altered the dimensional accuracy of your printed model. It’s worth experimenting with different tools, such as a deburring tool, which is often used. Sanding might also be helpful.
Because a brim is like the Goldilocks of adhesion assistants, it’s often considered the best overall choice. It provides some bed adhesion while still keeping material consumption and print time relatively low. As such, we suggest using a brim for models that are susceptible to bed adhesion issues (e.g. warping), such as large flat-bottomed models with corners. Using a brim for these types of prints will help keep them stuck to the bed while keeping filament usage and waste low (compared to a raft).
However, because brims directly affect the dimensional accuracy of the area of the first layer of your print, you might want to avoid using them when the accuracy of the printed model is important. This is usually the case for functional prints that are designed to be assembled with other objects.
On another note, you might also want to use a brim when you want to have a prettier print bottom rather than a rougher texture like the one you might see when you use a raft. Moreover, with a brim, your model’s bottom layer will match the texture of your build plate. So, if you’re printing on a glass bed, the model will have a very smooth bottom.
Lastly, we’re going over a few of the common slicer settings for brims. For consistency with our section for print settings for skirts, we’re using the latest version of Cura for the specific settings, but as noted, they’re very similar to the ones found in other 3D slicers, such as PrusaSlicer.
The most recent Cura update even added support for printing a brim of multiple materials in the same model.
Lastly, a raft is the third type of adhesion assistant, and we’re going over some important information about rafts as we have with the other adhesion assistants.
A raft is our third and final type of adhesion assistant. Of the three, it’s the most intensive when it comes to adhesion assistance, material consumption, and print time. Activating a raft adds a 3D printed base beneath your actual print. This base is multiple layers tall, and its area extends slightly beyond the maximum area of the first layer of your print.
The benefit of using a raft is that it provides great first-layer adhesion for any model because plastic sticks best to plastic. Additionally, because a raft’s area goes further than the area of your printed model, the amount of surface area that touches the build plate will always be greater with this adhesion type.
With a raft, your print doesn’t actually touch the print surface, so any inconsistencies with the build plate (e.g. dents) will likely only affect the raft instead of your model. And adhesion-related issues such as warping will also not affect your printed model as much and will mainly affect the raft structure.
Of course, because a raft is like a mini print inside of a print job, it takes a lot more filament and adds more print time than a skirt or brim. However, it might be worth it for some types of prints, which we’ll talk about next.
So when do you use a raft? Well, because it provides the most bed adhesion of all three forms of adhesion assistants, it’s best to use this feature for models where bed adhesion has been an issue. Rafts are especially helpful for securing the corners of a model down, so they work great for any rectangular or similarly designed models with sharp corners.
Of course, rafts are also very useful for models that have a limited surface area touching the print surface. Moreover, adding a raft will expand the area that touches the build plate, and your print’s first layer will form a better bond by sticking to the plastic raft than sticking to the build plate.
However, you should really only consider using a raft if you’re not concerned about material usage or print time because rafts add a lot of both. If you still need some bed adhesion help and want to limit the print time and material consumption, a brim may be the better alternative. This is especially true when warping at corners is the concern.
On another note, not only do rafts consume a lot of material, but they cause a lot of waste because the only thing you can really do with a raft is to throw it out – unless you have a filament recycler. And while rafts beat the others in terms of bed adhesion, they also often lead to not-so-pretty bottoms.
It’s also worth mentioning that rafts are the common adhesion solution for those printing in ABS. That’s because this material presents a lot of issues with bed adhesion and rafts are usually effective at solving these problems.
Additionally, it’s important to go over the print settings related to rafts, especially because they’re the most complex of the three adhesion assistant options. We’re going over the main Cura settings related to rafts below, but note that there are many more, as seen in the screenshot above.
Now that we’ve gone over skirts, rafts, and brims, it might also help you to know some other ways to keep the first layer of your prints secured to the print bed. Below are a few other methods for keeping your prints grounded:
License: The text of "Raft vs Brim vs Skirt: The Differences (incl. Cura settings)" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.