Helping the First Layer Stick Rafts, Skirts, and Brims — Annotated Notes & Key Takeaways

When a 3D print fails, the trouble often starts at the bottom. The first layer has to grip the build surface, and if it lifts, curls, or drags, everything above it is compromised. Slicers offer three common features that appear near the bottom of a print—rafts, skirts, and brims—and they are easy to confuse because they all involve extra plastic around the first layer. But they do different jobs, and understanding them is mostly about understanding first-layer adhesion and the small mechanical tricks that improve it.
 

The material treats these three features as tools for improving print quality and success rate, especially when the first few layers are the problem or when the part touches the bed over a very small area. That framing is useful because it keeps the focus on the actual failure mode. A raft, a skirt, and a brim are not interchangeable. They solve different problems, and choosing the wrong one can waste material, add cleanup time, or leave the original problem untouched.
 

What Each Feature Actually Does

A raft is a horizontal base printed underneath the part. It consists of a few layers of plastic laid down before the object itself begins. The raft is usually larger than the bottom footprint of the part, which gives the print more surface area to hold onto. That extra area helps with bed adhesion, and it also means the first layer of the actual part is being printed onto plastic rather than directly onto the build plate. Printing onto plastic can reduce spreading compared with printing onto the bed itself. If the filament is not water-soluble, the slicer leaves a small air gap between the raft and the part so the two can be separated after printing. That gap has to be tuned. If it is too large, the part may not stick to the raft well enough. If it is too small, removing the raft becomes difficult and may damage the bottom of the print. The material notes that rafts are primarily used with ABS, which is a material known for warping and adhesion trouble.
 

A skirt is a loop or several loops of plastic extruded around the outside of the part. It does not touch the part, and it does not extend underneath it. On the first layer, the skirt gives the extruder a chance to push filament through and establish a steady flow before the actual part begins. That priming effect is easy to underestimate. If the nozzle has been sitting idle, the first bit of extrusion can be inconsistent. A skirt gives the printer a place to get that inconsistency out of the way. A skirt can also be printed in multiple layers. In that case, it forms a kind of wall around the print that reduces air movement near the part. Less air movement means the print cools more slowly. That can matter for materials that are sensitive to drafts or rapid cooling. But the skirt itself is not attached to the part, so it does not directly improve adhesion. Its contribution to first-layer adhesion is indirect: it helps the extruder start cleanly, and a clean start means the first layer of the part has a better chance of going down evenly.
 

A brim is best understood as a skirt that touches the part. It is printed on the first layer and extends outward from the edge of the print by a set distance. Unlike a raft, it does not go under the part. It only adds surface area around the perimeter. That extra area gives the first layer more to hold onto, which is exactly what you want when the part has a small footprint or when the edges are prone to lifting. The material notes that brims are best used for parts with small first layers that fail to adhere properly. They are usually printed as perimeters rather than as a crosshatched infill pattern. That makes them easier to remove without damaging the part. A brim is not meant to be a permanent base. It is a temporary extension of the first layer that you peel away after the print finishes.
 

Why First-Layer Adhesion Is the Real Issue

All three features are responses to problems at the bottom of the print. The material makes that clear when it says they are used to improve quality and success rate, especially when prints fail on the first few layers or because the first layer is small. That is the common thread. A raft helps by giving the part a larger plastic base and by letting the first layer of the part sit on plastic instead of the bed. A brim helps by increasing the surface area of the first layer itself. A skirt helps by making sure the extruder is primed and the flow is stable before the part begins. They attack the same general problem from different angles.
 

The distinction between a skirt and a brim is the one that seems to trip people up most often. Both go around the part. Both are printed on the first layer. The difference is contact. A skirt stands off from the part. A brim touches it. That single difference changes everything. A skirt cannot hold the part down because it is not attached. A brim can hold the part down because it is attached and it widens the footprint. If your problem is that the first layer is not sticking, a skirt will not solve it directly. If your problem is that the extruder is not primed and the first line of the part is thin or missing, a skirt can help. If your problem is that the part has a tiny bottom surface and keeps peeling up, a brim is the more direct tool.
 

A raft sits in a different category because it goes underneath. It is not just an extension of the first layer. It is a separate base that the part is printed on top of. That makes it more invasive. It uses more material, it adds print time, and it requires a separation gap that has to be tuned. In exchange, it can provide a very strong grip for materials that struggle to stick. The material specifically mentions ABS as the primary use case. ABS is notorious for warping, and a raft can help hold the part down while the lower layers cool. But the raft also changes the bottom surface of the part. The first layer of the part is not the bottom of the print anymore; the raft is. That can affect surface finish and dimensional accuracy at the bottom.

A skirt, by contrast, is the least invasive. It does not touch the part, so it does not change the part’s dimensions or surface finish. It does not need a separation gap. It does not add much material. Its main job is to get the extruder ready. That makes it a reasonable default for prints that do not have a specific adhesion problem. It is also useful when you want a little extra cooling control. A multi-layer skirt can act as a windbreak, slowing the cooling of the print. That can be helpful for ABS or other materials that benefit from a warmer, more stable environment. But again, it is not a adhesion fix. It is a priming and cooling tool.
 

How to Choose Between Them

The choice comes down to what is actually failing. If the first layer is not going down because the extruder is not primed, a skirt is the right starting point. It gives the nozzle a chance to establish flow before the part begins. If the first layer is going down but the part is peeling up at the edges, especially on a small footprint, a brim is the better choice. It adds surface area where it is needed most. If the part is large, warp-prone, and refuses to stay flat even with a brim, a raft may be necessary. The material frames rafts as a tool for bed adhesion issues, primarily with ABS. That suggests they are a heavier solution for a more stubborn problem.
 

There is also the question of removal. A skirt is the easiest to remove because it never touches the part. It just lifts away. A brim is attached to the first layer, so it has to be cut or peeled off. If the brim is printed as perimeters, it usually comes away cleanly, but it still leaves a seam or a rough edge that may need sanding. A raft is the most involved. It has to be separated from the bottom of the part, and the separation gap determines how easy or difficult that is. If the gap is wrong, you can end up with a raft that will not let go or a part that detaches from the raft during printing. The material notes that this gap needs to be adjusted to balance adhesion and removability. That is a tuning step that neither a skirt nor a brim requires.
 

Material choice also matters. The material says rafts are primarily used with ABS. It does not say that brims or skirts are limited to any particular filament. That makes sense. Priming and surface area are general concerns. But ABS is a special case because it warps and shrinks. A raft can help hold it down, and a multi-layer skirt can help keep the cooling gradual. PLA, PETG, and other materials may need less intervention. A brim may be enough for a small PLA part. A skirt may be enough for a well-calibrated printer with a clean bed. The material does not give a decision tree, but the logic is there: start with the least invasive fix and escalate only if the problem continues.
 

One point that could use more explanation is how these features interact with the rest of the first-layer settings. The material mentions that a raft has a separation gap and that a brim is usually printed as perimeters. It does not mention layer height, extrusion width, bed temperature, or first-layer speed. Those settings also affect adhesion. A brim on a poorly leveled bed may not help. A skirt on a bed with inconsistent Z-offset may not prime correctly. The material treats the three features as if they are the main variable, but in practice they are one part of a larger first-layer setup. That is not a flaw in the material so much as a limitation of its scope. It answers the question it was asked, but it leaves the broader calibration picture untouched.
 

Limits, Gaps, and What the Material Leaves Unsaid

The material is short and focused, which is both a strength and a limitation. It explains what each feature is and what it does, but it does not give specific numbers. There is no recommended air gap for a raft, no suggested brim width, no skirt offset, and no layer count. That means a reader still has to experiment or look elsewhere for starting values. The material also does not compare the surface finish of a raft-printed bottom versus a brim-printed bottom. It mentions that a raft allows the bottom layers to contact plastic rather than the bed, which reduces spreading, but it does not say whether that improves or worsens the visual quality of the bottom surface. That is an open question.
 

Another gap is the distinction between water-soluble and non-water-soluble filament for rafts. The material says that if non-water-soluble filament is used, an air gap is placed between the raft and the print. That implies that water-soluble filament might be used differently, perhaps as a dissolvable interface. But the material does not explain how that works or when it is useful. A reader who wants to use a dissolvable raft interface would need more information. The material also does not discuss dual-extrusion setups, which are often used for soluble supports and rafts. That is outside its scope, but it is a natural follow-up question.
 

There is also the question of modern slicer defaults. Many slicers now default to a skirt for every print, and some users never change it. A brim is often hidden in an adhesion submenu. A raft is sometimes treated as a legacy feature. The material does not address how these features are presented in different slicers or how their default settings behave. That is a practical gap for a beginner who is trying to find the right checkbox. The material assumes the reader already knows where these features are and what they are called. That is reasonable for a technical reference, but it means the article is not a complete beginner’s guide.
 

The material also does not discuss the mechanical reason why a brim improves adhesion. It says that a brim increases the first layer surface area, which gives more area to adhere to the bed. That is true, but it is not the whole story. A brim also reduces the effect of shrinkage at the edges of the part. When the part cools, it contracts, and the edges want to pull inward. A brim adds material that resists that pull. The material does not mention shrinkage or warping mechanics in that level of detail. It just says that a brim helps adhesion. That is enough for a basic answer, but it leaves the reader without a deeper understanding of why it works. The same is true for the skirt’s cooling effect. The material says a multi-layer skirt reduces air movement so the print cools slower. It does not explain how much slower or what materials benefit most. That is left to the reader’s judgment.
 

One more limitation is the absence of failure modes. The material does not say what happens if a raft is too thin, or if a brim is too wide, or if a skirt is too close to the part. It does not warn about the brim fusing to the part so tightly that removal damages the print. It does not mention that a raft can make the bottom of the part look rough or that a brim can leave a visible lip. These are practical concerns that a reader will encounter. The material gives the concepts but not the troubleshooting. That is a gap worth noting.
 

Practical Takeaways for Your Next Print

If you are trying to decide which feature to use, start by identifying the failure. Is the first layer missing or thin at the start? That is a priming problem, and a skirt is the simplest fix. Is the first layer going down but lifting at the corners? That is an adhesion problem, and a brim is the next step. Is the part large, warp-prone, and refusing to stay flat even with good first-layer settings? That is when a raft becomes worth the extra material and cleanup. The material’s description of rafts as primarily for ABS is a useful clue. ABS is the material most likely to need that level of intervention. Other materials may never need a raft at all.
 

When you use a brim, keep it as perimeters rather than infill. That makes it easier to remove without gouging the part. When you use a skirt, consider whether a single loop is enough for priming or whether multiple loops would help with cooling. When you use a raft, spend time tuning the separation gap. Too much gap and the part will not stick to the raft. Too little gap and the raft will not come off. That tuning is part of the cost of using a raft. It is not a set-and-forget feature.
 

It also helps to remember that these features are not mutually exclusive in concept, even if slicers usually treat them as separate options. A skirt can be used alongside a brim if you want priming and extra adhesion. A raft already includes a brim-like base, so adding a separate brim may not make sense. The material does not discuss combinations, but the logic of each feature suggests where they overlap. The main thing is to avoid using a skirt when you actually need a brim, or a brim when you actually need a raft. That is the most common mistake. The names sound similar, but the jobs are different.
 

The final takeaway is that first-layer adhesion is not one problem. It is a family of problems: priming, surface area, cooling rate, and warping. A skirt addresses priming and cooling. A brim addresses surface area and edge shrinkage. A raft addresses all of them at once, but at the cost of material, time, and cleanup. The material gives you the vocabulary to tell these apart. The rest is testing on your own printer, with your own filament, on your own bed. That is where the real answers come from.