Brim, skirt or raft: what do you need when in 3D printing?
are explained briefly when you hover over or tap them.
Brim, skirt and raft are three helper structures that the slicer prints around or under your part. They look similar but have very different jobs. Anyone who mixes them up wastes material or keeps struggling with parts that come off the bed.
The three at a glance
| Skirt | Brim | Raft | |
|---|---|---|---|
| What is it? | line around the part with a gap | flat edge directly against the part | multi-layer platform under the part |
| Touches the part? | no | yes, in the first layer | yes, the part sits on it |
| Main purpose | prime the nozzle, check the first layer | more adhesion area against lifting | level out unevenness, very small contact area |
| Material use | very low | low | high |
| Effect on the underside | none | small ridge at the edge | rougher underside |
| Needed today? | optional | often useful | rarely |
Skirt: for priming
A skirt is one or more lines that run around the part with some distance. It has no connection to the part and does not help with adhesion.
What it is good for:
- The nozzle builds up pressure before the actual part starts.
- After just a few seconds you can see whether the first layer is right. What it should look like is covered in First layer not sticking.
Typical values: 1 to 3 lines, 3 to 6 mm distance from the part, one layer high. Many current printers print a purge line at the edge of the bed before every print anyway. In that case the skirt can be dispensed with, and some manufacturer profiles therefore have it off by default.
Special case: draft shield
Some slicers can extend the skirt over the full height of the part (in PrusaSlicer “Draft shield”). It shields the part from draughts and can help with ABS and ASA in open printers. It does not replace an enclosed build chamber.
Brim: against lifting
A brim is a flat edge made of several lines that sits directly against the part in the first layer. It enlarges the contact area exactly at the edges, where the forces are greatest as the part cools. After printing you peel it off.
When you need it:
- material with high shrinkage such as ABS, ASA, nylon or PC
- large, flat parts with sharp corners
- tall, narrow parts with a small footprint
- small individual parts that come loose easily
Typical values:
| Setting | Value |
|---|---|
| Brim width | 3 to 5 mm for PLA and PETG, 5 to 10 mm for ABS, ASA, PA, PC |
| Distance to the part | 0 to 0.1 mm, larger means easier to remove but less hold |
| Type | outside only |
Prusa recommends at least 3 mm, and the Bambu Lab standard profiles use 5 mm. A brim on inner contours (for example in holes) is hard to remove and achieves little. Leave it on the outside.
With warping problems the brim is only one building block. The environment is often more important, see Warping.
Mouse ears
Mouse ears are small round brim discs only at the corners. They hold exactly where a part lifts first, save material and are quicker to remove than a full brim. Straight edges stay clean.
OrcaSlicer can place mouse ears automatically at sharp corners. You set an angle to define from which corner an ear is created. In other slicers you can place small discs as separate objects at the corners or paint the brim only on certain spots.
Raft: rarely needed today
A raft is a multi-layer platform. First the printer prints a few thick base layers, then a finer contact layer on top, and only then the part. A small gap remains between raft and part so that they can be separated.
In the past a raft was often the default because print beds were uneven, poorly heated or not mapped. Today most printers have heated spring steel plates with a PEI coating and automatic bed mapping. That makes a raft unnecessary in most cases.
A raft still makes sense:
- for parts with a very small or irregular contact area, such as figures on thin feet
- when a part stands on supports and the supports themselves need hold
- with very strongly warping materials when a brim is not enough
Disadvantages: significantly more material and time, a rougher underside and often inaccurate dimensions at the bottom. The distance between raft and part corresponds to that for supports. More on this in Supports.
Decision guide
- Does the part hold well without help and is it made of PLA or PETG? Then nothing, at most a skirt.
- Does it lift at the corners or is it tall and narrow? Brim or mouse ears.
- Material with high shrinkage? Brim, plus an enclosed build chamber.
- Tiny or irregular contact area? Raft.
If, on the other hand, a part sticks too well, Print comes loose helps.