Extrude, inset and loop cut

Extrude, inset and loop cut are the three operations you will use most when building a mesh by hand. Extrude pulls new geometry out of what you select, inset makes a border of faces inside a selection, and loop cut adds a new edge loop across a strip of faces. Almost every shape in box modeling is made by repeating these three.

#Extrude

Blender's manual defines it as follows: "Extrusion tools duplicate vertices, while keeping the new geometry connected with the original vertices" (Blender Manual: Extrude Region). A vertex extrudes into an edge, an edge into a face; extruding a rectangle makes a box and extruding a circle makes a cylinder (Blender Manual: Extrude Region).

When you extrude a region of faces, only its outer border grows new side walls; the inside moves as one piece. By default the faces move along their averaged normal (Blender Manual: Extrude Region). As a result, one extrude on a flat panel gives a clean raised block with no internal faces.

#Inset

Inset "creates a border of faces around the selected faces": as the border grows, the outer faces shrink and the inner faces keep their size (Blender Manual: Inset Faces). The main settings in Blender are Thickness (the width of the border), Depth (raising or lowering the inner faces), Outset (growing the border outward instead) and Individual, which insets each face on its own rather than each connected patch as one unit (Blender Manual: Inset Faces). Offset Even, on by default, keeps the border the same width all the way round (Blender Manual: Inset Faces).

Inset on its own is rarely the goal. It prepares a face for an extrude: the border becomes the frame, the inner face becomes the panel.

#Loop cut

Loop Cut and Slide "splits a loop of faces" into two or more parallel loops; you hover over an edge at right angles to the cut you want, click, then slide the new loop into place (Blender Manual: Loop Cut and Slide). You can add several cuts at once, and the Even option keeps the new loop at an equal distance from one neighbour instead of a proportional one (Blender Manual: Loop Cut and Slide).

The cut follows a face loop around the mesh. It stops where the loop stops: at poles, because "there is no unique way to continue a loop from a pole" (Blender Manual: Structure). If a loop cut ends somewhere unexpected, look for a pole, a triangle or an N-gon in its path.

Loop cuts are also how you add support loops for subdivision surface modeling: slide a new loop close to an edge and the subdivided corner gets tighter.

#Use in The Last of Us Part I

On The Last of Us Part I, Matthew Trevelyan Johns modeled props with "hard edges and 90-degree angles", the kind of shapes extrude and inset produce, with the bevel supplied by a baked-bevel trim in the normal map rather than by extra edges, which saves polygons (ArtStation: The Last of Us: Part I...Trim Pipeline). He estimates about 80% of his Lab assets were made this way instead of with unique high-to-low bakes (ArtStation: The Last of Us: Part I...Trim Pipeline). In this approach, extrudes and insets define the form and the texture supplies the edge detail.

#What these operations do to topology

Every extrude and inset adds edges at the corners of the selection. On a flat quad grid, extruding a face up adds a fifth edge to each of its four corners, which makes them 5-edge poles (see pole). Inset adds a diagonal edge at each corner for the same result. On a low-poly prop this does not matter. On a subdivision cage, those corners are where you check for pinching.

#In different tools

Other modelers have their own versions of these tools under their own names; this page uses Blender's because its manual is public. In Blender they are Extrude Region (E), Inset Faces (I) and Loop Cut and Slide (Ctrl-R) (Blender Manual: Extrude Region; Blender Manual: Inset Faces; Blender Manual: Loop Cut and Slide). See modeling software for the alternatives.

#Related terms

box modeling · edge loop · face loop · support loop · pole · bevels and chamfers

#Further reading and watching