How to subdivide in Blender: Subdivide, Subdivision Surface and Loop Cut

Subdividing means adding geometry to an object: to smooth it, to sculpt details into it, or to have vertices where there are not enough. Blender offers three tools that look alike but do not do the same thing. This guide explains which one to choose, and how to keep sharp edges on a smoothed object.

Three tools, three uses

Subdivide: cutting faces in Edit Mode

1. Select the object and switch to Edit Mode (Tab).
2. Select the faces or edges to cut (A to select everything).
3. Open the Edge menu, then Subdivide.
4. Adjust the result in the panel that appears at the bottom left (Adjust Last Operation).

The options you will use most:

• Number of Cuts: the number of cuts per edge. One cut splits the edge in two, two cuts in three. A square face with its four edges selected becomes four squares with one cut.
• Smoothness: moves the new vertices so that they roughly follow the curvature, instead of staying flat.
• Create N-Gons: when unticked, it forces triangles and quads instead of faces with more than four sides.
• Fractal and Along Normal: move the vertices randomly, or along their normal, for an irregular relief; Random Seed changes the random pattern.

Subdivide changes the mesh for good: use it to add vertices at a precise spot before extruding or deforming, as in the guide to extruding (in French).

The Subdivision Surface modifier: smoothing without destroying

In Object Mode, Ctrl+1, Ctrl+2 or Ctrl+3 adds the Subdivision Surface modifier (glossary entry in French) with the matching level in the viewport, or changes the level of an existing modifier. You can also add it through Add Modifier, Generate. The base mesh stays light and editable; the modifier computes the smooth surface on top of it.

• Catmull-Clark or Simple: Catmull-Clark subdivides and rounds; Simple subdivides without smoothing, which is useful for densifying a mesh before a displacement.
• Levels Viewport and Render: the level in the 3D Viewport and the level at render time. The shortcuts only change the first one: check the Render level before starting a render.
• Optimal Display: hides the edges created by the subdivision in wireframe view.
• Use Creases: takes into account the creases given to edges (see below).

The manual warns that high levels greatly increase memory use and can freeze Blender. Level 1 or 2 in the viewport is almost always enough to work with. To smooth the shading without adding geometry, Object, Shade Smooth is sometimes all you need.

Loop Cut: adding an edge loop

1. In Edit Mode, press Ctrl+R.
2. Hover over an edge: the loop that crosses it is shown as a preview.
3. Scroll the mouse wheel to add cuts, spaced evenly.
4. Click to confirm, then slide the loop to where you want it and click again. A right click leaves it in the centre.

Loop Cut only works well on quad topology: a triangle or a face with more than four sides stops the loop. That is one more reason to keep a clean mesh, as the entry on the mesh in Blender (in French) explains.

Keeping sharp edges on a subdivided object

With Subdivision Surface, a cube turns into a soft ball. Two techniques hold the edges:

• Support loops: a Loop Cut placed close to an edge tightens the curvature there. The closer the loop, the sharper the edge.
• Creases: select the edges in Edit Mode, press Shift+E and raise the value towards 1. The edge then resists smoothing without adding geometry.

The Bevel modifier (in French), placed before Subdivision Surface, is a third solution for even, rounded edges.

Subdivision and rendering

Subdivision comes at a cost at render time: each level multiplies the number of faces. For an object far from the camera, a low render level is enough. In Cycles, adaptive subdivision adjusts the level according to the distance from the camera, which is mostly useful with a displacement texture. The keys used here are gathered in the Blender shortcuts guide.