A brim is a single-layer flat area around the base of your model. Its purpose is to keep the edges of your print down and make the contact area between your print and the build plate bigger.
The brim parameters are in the Other group on the left sidebar. They are all per-object parameters, so you can set different values for each object.
It is a new feature designed by Bambu Lab. In this mode, Bambu Studio automatically analyzes each part of each individual object and generates a brim with the proper width for it. The following factors are mainly considered:
A taller part with a smaller footprint usually needs a wider brim to prevent itself from being toppled by the printer's nozzle during printing. A taller part with a smaller footprint is easily detached from the heat bed as the part is cooling down and therefore needs a wider brim.
A part with the material type PC, ABS, PA-CF, PET-CF, or PLA-CF usually results in a wider brim, since those materials have high thermal expansion factors and high molding temperature which results in high thermal stress at the foot of the part. On the contrary, a TPU part usually needs a narrower brim.
The maximum printing speed usually means larger shear forces between the hot end and the parts and therefore needs a wider brim to stick the parts on the heat bed.
In addition to auto mode, you can also choose several other types of Manual Brim. Bambu Studio will generate Brim based on the "Brim width" parameter, which users can set according to actual situations. Manual Brims are divided into the following types:
Generate Brim only around the outside of the object:
If the inside of the object is hollow, Brim is generated only around the inside of the object
Note: The inside brim can only be generated if the object itself has holes inside. If the object has no holes inside, or if it is only specially set to be hollow inside (such as using the Negative parts function), it will not be able to generate an inner brim after slicing.
Brim will be generated around both the inside and outside of the object:
No brim will be genrated.
The desired width of the generated brim in Manual mode.
The desired gap between the object and its brim in both "Auto" and "Manual" modes. A smaller gap can improve the connection strength while a larger gap will make disassembling easier. If you set the gap to 0 and find that there is still a gap between Brim and the model, it is usually caused by turning on the "Elephant foot compensation" function. You can disable “Elephant foot compensation” to make Brim fully attached the model. The comparison is shown in the following figures: