The Raft, Skirt and Brim elements are three additional elements that can be configured during slicing and are generated and added to the piece automatically.
Although the three elements are often placed in the same category in slicing software, their function is different.

Raft

The raft consists of a platform that is created between the base and the workpiece. It consists of two parts: the base contact zone and the part contact zone.

The base contact zone is generated from a line structure with a low density of infill. It is created by means of thick layers and over-extrusion, which favors adhesion to the base and allows the heat of the platform to be diffused. Its function is twofold: on the one hand, it compensates for imperfections in the printing base and, on the other, it improves the adhesion of parts prone to warping. It is a common element when printing ABS or ASA.

Image 1: A piece 3D printed with a Raft. Source: Filament2print.com

Its main disadvantage is that if the separation of the part is not configured correctly, it can be difficult to separate it. It is not recommended for materials with good adhesion between layers, such as PETg.

Skirt

This is a perimeter that is printed around the part. Its height can range from a single layer to the full height of the part.

It is generally only used on the first layer in order to purge the extruder before printing begins.

Image 2: A piece 3D printed with the skirt at full height. Source: Filament2print.com

Sometimes the skirt can be used for the full height of the part in order to build up a wall to protect the part from draughts and to keep the heat in. This is very helpful on materials that exhibit warping such as ABS or Nylon.

A special type of skirt, called a wiper wall, is used in some laminating software to purge the extruder during material changes. This element has a lower material consumption than the cleaning tower, but it is much more unstable, so it is not recommended for use on high parts or when using soluble support material.

Image 3: A two-color 3D printed piece with a wiper wall around it. Source: Raise3D

Brim

This consists of extending the first layer around the perimeter. It is mainly used to improve the adhesion of the part to the base. It is very useful in parts prone to warping with sharp corners or parts with very little contact surface with the base. It has the disadvantage that, once the printing is finished, it must be removed mechanically.

Image 4: A 3D printed piece with a brim. Source: Filament2print.com

Most slicing software allows the use of a combination of skirt and raft, which can make it easier to print ABS or Nylon on open printers, reducing the effect of warping.

This guide discusses the concepts in a general way and does not focus on a particular make or model, although they may be mentioned at some point. There may be important differences in calibration or adjustment procedures between different makes and models, so it is recommended that you consult the manufacturer's manual before reading this guide.