Brim VS Raft VS Skirt: Everything You Need to Know

Bed adhesion is one of the largest problems with 3D printing and getting the first layer of your models to stick to the build plate can be a challenge. There are many ways to improve bed adhesion – using glue, heating the bed – but one of the most effective is to use an adhesion assistant.

An adhesion assistant is a term we’ve given to the three build plate adhesion types, including skirts, brims, and rafts, that can be found in most 3D slicers, like Ultimaker Cura and PrusaSlicer. 

Each of the three types of adhesion assistants offers its own benefits and disadvantages that make them most useful in different scenarios.

We can think of skirts, brims, and rafts as the three bears from Goldilocks. A skirt offers the least adhesion with the least costs, a raft provides the most adhesion but at the most costs, and a brim is a good middle-ground option. 

A skirt is likely the best way to go when you just want a way to test that your bed is level and extrusion is good, but don’t need any adhesion help. A brim is perhaps the best option when you want some bed adhesion help but don’t want to use too much extra filament. Lastly, a raft is for those who don’t really care about how much filament they use or the length of the print, but simply want the most bed adhesion help for the highest quality print.

Want to learn more about skirts vs brims vs rafts? 

Read on as we go over each option when to use it, the popular slicer settings for each option, and more! 

Enjoy!

What is a Skirt?

First up, we have the skirt. A skirt is the least intensive form of adhesion assistant and it’s a perimeter that goes around the first layer of a model. A skirt is always only one layer tall, but it’s usually a few walls thick, meaning there are a few nozzle passes (print lines) that make up the skirt.

What’s most important to know about a skirt is that it doesn’t actually touch the first layer. This means, despite being called an adhesion assistant, it actually provides no help with a print’s bed adhesion because it technically is a separate entity on the print surface. 

Nonetheless, because a skirt, as well as any of the other bed adhesion assistants, prints before your actual print, it still helps with a few things. Moreover, a skirt is a great indicator of your printer’s extrusion and you can look at the skirt to make sure that filament is flowing out of the nozzle properly. Additionally, because a skirt extends around the area where your model will be printed, you can see how it turns out to gauge how level the bed is and adjust it accordingly.

When to Use a Skirt?

So, now that you know what a skirt is, you’re probably wondering when it’s best to use this form of adhesion assistant. 

A skirt is the best option when you’re not too concerned about your model’s bed adhesion, but still want to check that your printer is working (e.g. extrusion, bed levelness) before your real print actually begins. 

Of course, the other adhesion assistant options (brim and raft) also can indicate if your printer is working properly before the print. However, a skirt does this while using the least amount of filament and adding the least print time compared to the other options.

Skirt Slicer Settings

As we mentioned, the three types of bed adhesion assistants are slicer features and once activated, there are a few different settings for skirts that control how they are printed. In this section, we’ve gone over the main slicer settings for skirts that you can use to adjust how they come out on prints.

Source: Youtube ModBot

Skirt Line Count

The first skirt-related slicer setting is the skirt line count, which controls the number of passes the nozzle will make while printing the skirt. In other words, it defines the width of the skirt, so the larger this value, the wider your skirt will be, and the more filament and time it will take. A skirt line count of 3 or 4 works great for most prints.

Skirt Distance

Second, the skirt distance is the distance that separates the inner-most skirt line from the first layer of the print. The larger this value, the further away your skirt will be from your actual print, which reduces the amount of print space you have to work with. 10 mm is the default skirt distance in many slicer programs and it works fine, but if you want to conserve more build plate space, consider lowing it a little bit (e.g. 5 mm).

Skirt Minimum Length

Lastly, the skirt minimum length, as the name suggests, is the minimum length that the skirt has to be for it to be printed at all. 250 mm for the minimum length works great!

Advantages and Disadvantages of Using a Skirt

Lastly, for our overview of skirts, we’ve listed the advantages and disadvantages of this type of bed adhesion assistant in the bulleted lists below:

Advantages:

  • Checks that the nozzle isn’t clogged, the bed is level in the printing area, and the extruder and hot end are working
  • Uses very little filament
  • Adds very little time to a print job
  • Very easy to set up and configure in your slicer

Disadvantages:

  • Reduces the usable area on the build plate
  • Doesn’t provide any bed adhesion assistance

What is a Brim?

A brim is our second most intensive form of adhesion assistant and is similar to a skirt, but it directly attaches to the first layer

Moreover, a brim is one layer tall and is a perimeter that goes around the entire first layer area of a print. Additionally, a brim is made up of a few walls, with each nozzle pass going closer to the first layer of the print.

The final wall of the brim is connected to the first layer. This allows the brim to actually expand the bottom surface area of your print that attaches to the build plate, thus making the part more likely to stick to the print surface and stay attached throughout the printing process.

Usually, a brim will be wider (more walls) than a skirt because the goal of a brim is mainly to help secure the print to the bed, while a skirt’s goal is to prepare the extruder. Due to the wider size of a brim, it consumes more filament and also adds more print time than a typical skirt. 

That said, you will have better bed adhesion with a brim.

When to Use a Brim?

Because it’s more focused on making your print stick to the bed, a brim is best used when your model doesn’t have a large surface area touching the build plate (i.e. printing a figurine where only the feet of the model touch the 3D printer bed). 

That’s because, as we explained, a brim expands the bottom surface area, so your print will be less likely to detach from the build plate throughout the printing process.

Of course, you might be thinking that a raft, which we’ll discuss later, is the better option for these types of prints because it provides the most bed adhesion. 

That would be correct, but a brim consumes significantly less material and adds a lot less print time compared to a raft that many users go-to option for bed adhesion assistance

Overall, a brim is the Goldilocks of bed adhesion assistant, so we suggest using it when you want better print surface adhesion for a print and also want to conserve filament and keep print time low.

Brim Slicer Settings

There are a few different slicer settings for a brim that allow you to control how it’s printed. In this section, we’ve gone over a few of the most popular ones from a few different slicer programs, like Cura and PrusaSlicer.

Source: Youtube ModBot

Brim Width

The first and perhaps most important slicer setting related to a brim is the brim width. As the name indicates, this setting measures, in millimeters, the width of the brim. The brim width also directly controls the brim line count, which defines how many nozzle passes the printer makes to achieve the brim width. A width of 8 mm provides excellent bed adhesion for prints, but for parts that are still facing adhesion issues, consider using an even higher value.

Brim Minimum Length

Another slicer setting for brims is the brim minimum length. This setting controls how small a brim is able to be and if the expected brim length doesn’t meet or surpass this value, it won’t be printed. For this setting, you can use the 250 mm, which is the same value as our recommended skirt minimum length.

Brim Only on Outside

Our last brim setting is called “Brim Only on Outside” and is an activatable option that controls whether brims can be printed on inside features of a model. For example, let’s say you’re printing a hollow cylinder. Turning this setting off will allow the printer to make a brim on both the inside and outside of the cylinder hole. We suggest not turning this setting on as you probably want a brim to help as much as possible with bed adhesion.

Advantages and Disadvantages of Using a Brim

Next, we’ve listed the pros and cons of a brim in the bullet points below to give you a summary of the bed adhesion assistant option:

Advantages:

  • Doesn’t use too much filament
  • Doesn’t add too much time to a print job
  • Adds a decent amount of adhesion by expanding the surface area of a print touching the build plate
  • Is very easy to control with slicer settings

Disadvantages:

  • Uses more filament than a skirt
  • Adds more time to a print than a skirt
  • Reduces the usable area on the build plate
  • Doesn’t provide the most bed adhesion compared to a raft

What is a Raft?

Our last form of bed adhesion assistant is a raft. A raft is the most intensive form of slicer adhesion assistant and it doesn’t just act as a perimeter that goes around the first layer area of a print, but rather is an entirely separate print. Furthermore, a raft is a rectangular structure that extends past the first layer’s X/Y area and is a few layers tall.

The best way to think about a raft is like you’re printing a mini build plate beneath every print.

The reason rafts are the most helpful of the three-bed adhesion assistants is because a raft is made of the same plastic as your printed model. And, plastics stick best to the same plastics so you will have better bed adhesion compared to if your print was sticking to your metal or glass build plate. 

This means you don’t have to use glue or any additional adhesive to achieve a great first layer on your desired print.

Source: Youtube ModBot

Another reason for a raft’s great adhesion is because it separates the build plate from the print. This means any build plate-related issues like a dent in the bed or slight unlevelness will not be as significantly reflected in your print. That’s because the raft structure will absorb these issues while still providing a flat, even, and adhesive surface for your actual print to stick to.

Of course, because a raft is an entire mini print beneath your actual print, it uses a lot of extra filament. As you might expect, adding a raft to a print also extends the print time significantly.

When to Use a Raft?

As we explained, a raft takes up a lot of extra material and adds a lot of print time to your print jobs. 

For this reason, we suggest only using a raft when print time and filament usage aren’t a concern at all and you have a model that won’t seem to stick. Moreover, you should especially consider using a raft when printing models that are skinny and have only a small surface area touching the build plate.

A raft is also the go-to bed adhesion assistant choice for many users printing temperature-sensitive materials like ABS and ASA. That’s because a raft reduces the chances of bed adhesion issues like warping, which are common with ABS and ASA, from affecting the actual print model.

Raft Slicer Settings

As a raft is the most complex of the three-bed adhesion assistants we’ve gone over, it makes sense that there are the most slicer settings for a raft. In this section, we’ll go over a few of the main ones.

Source: Youtube ModBot

Raft Base Thickness and Top Layers

The first settings we’ll go over are the raft base thickness and the raft top layers and these settings control the height of the raft. The former defines the size, in millimeters, of the initial layers of the raft, while the latter controls how many additional layers are printed on top of the initial bottom layers. Raising either one of these values will increase the number of layers used on the raft.

So how many layers work best for a raft? 

Well, there’s no one set number of layers that’s best for every printer and model, but somewhere in the range of 3-6 layers should work great.

Raft Print Speed

Another setting is the raft print speed, which is how fast the different features of a raft, like the walls and top layers, are printed. Similar to how you want to print your first layer slower than the raft, you’ll want to use a pretty low speed setting for your raft, like 20-30 mm/s.

Raft Air Gap

The raft air gap is another important setting and it defines the separation distance between the last layer of your raft and the first layer of your print. The larger this value is, the further away your printed model will be from the raft and the less effective it is for bed adhesion. However, don’t use too low of a value or you won’t be able to remove your print from the raft easily. 0.3 mm for the raft air gap should work great!

Raft Extra Margin

Our last setting for rafts is the raft extra margin. This setting controls how much X/Y distance the raft extends past the first layer area of your print. Using a larger value will expand the surface area of your print that’s attached to the build plate but will also significantly increase filament usage and print time. 10-20 mm for this value should work fine, but it depends on the size of your printed model.

Advantages and Disadvantages of Using a Raft

Finally, to summarize the good and bad of using a raft, we’ve listed the feature’s advantages and disadvantages below:

Advantages:

  • Provides the most adhesion to prints
  • Reduces the effects of build plate issues like a dent in the build plate
  • Lessens the chances of bed adhesion issues like warping from affecting prints

Disadvantages:

  • Leaves a rough texture on the bottom of prints
  • Uses a lot of filament
  • Adds a lot of time to the print job
  • Reduces the usable area on the build plate
  • Wasteful because you will likely throw away the raft structure
  • Can make print removal difficult

Difference Between a Brim, a Raft and a Skirt

Now that we’ve gone over skirts, brims, and rafts, you may be wondering what the actual differences between the three are. In this section, we’ll go over this!

The best way to distinguish the three-bed adhesion assistants is thinking of them as they’re on an X/Y graph, where the X-axis measures bed adhesion (further right equals more bed adhesion) and the Y-axis measures material usage (higher up equals more filament used). 

The brim, raft, and skirt all lie on a diagonal line that covers the X/Y graph, but the raft is furthest up and to the right, the brim a little less so, and the skirt closest to the origin of the graph.

For a less math-y answer, a raft provides the most bed adhesion but at the cost of the most filament usage and extra print time compared to the other options. The brim is a good mix of bed adhesion assistance and material usage and print time. Lastly, the skirt provides no adhesion assistance but helps prime the extruder and uses a very little filament, thus adding a small amount of time to the print job.

Conclusion

Overall, a skirt, brim, and raft are all great options for a bed adhesion assistant and they each are best for different situations.

A skirt is likely the best way to go when you just want a way to test that your bed is level and extrusion is good, but don’t need any adhesion help. A brim is perhaps the best option when you want some bed adhesion help but don’t want to use too much extra filament. Lastly, a raft is for those who don’t really care about how much filament they use or the length of the print, but simply want the most bed adhesion help for the highest quality print.

No matter which option you go with, though, you can use the slicer settings to achieve the best results. 

Enjoy!

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