Building Topology: Extruding and Merging Edges

Once you have initial polygons, you can grow your mesh organically by extruding edges. Edge extrusion creates new polygons by extending existing edges outward, automatically placing new vertices on your reference surface. This is one of the fastest ways to build topology.

How to do it:

You're likely already familiar with the process of dragging a vertex point (below, left) or a polygon edge (right) and how this will skew your near-proximity polygons.

Edge extrusion adds new retopo geometry onto the current polygons.

Hold Alt and click-drag from an edge to extend it (shown below). Releasing the mouse button confirms the new polygon.
While still dragging with Alt+dragging with the mouse button held down, tap Alt again to toggle between two additional extrusion modes.
- Edgeloop extrusion: Extends only the selected side, a matched number of new polygons.
- Polyloop extrusion: Extends the entire loop of connected edges. Again, note how all of this additional geometry is created by simply dragging a single polygon edge (circled below).
Edgeloop extrusion via Ctrl: Alternatively, you can build new topology from polygons with the control (Ctrl) key. To do so, begin with some existing retopo geometry, such as a patch:
From here, grab an edge segment and drag while holding the Alt key, like so:
Now, while keeping your mouse button depressed, release the Alt key and hold down the Ctrl key. Drag the mouse from side to side to increase or decrease the number of edgeloops in your temporary geometry.

Still without releasing your mouse button or the Ctrl key, drag the mouse up and down to extend your geometry laterally.

Why you'd use this:

This toggle gives you precise control over whether you're building topology locally (for detail areas) or extending entire sections (for broad coverage). The ability to switch modes mid-stroke without releasing your pen makes for an extremely fluid workflow. For example, you might start extruding a single edge around a nostril, then tap Alt to switch to loop extrusion mode to quickly build out the rest of the nose area.

Moving vertices and edges

After creating topology, you'll likely reposition vertices and edges to refine polygon flow and ensure proper alignment with your reference model's features.

To reposition your topology:

Moving vertices: Click and drag vertices to new positions. Brush size determines how many vertices move together.
Moving edges: Click and drag edges to adjust polygon flow.
Moving faces:Click and drag polygon faces to alter a given polygon and the polygons near it.

Why you'd use this:

Topology rarely comes out perfect on the first pass. Moving vertices allows you to adjust edge flow to follow muscle structure, anatomical landmarks, or surface contours. The Alt-toggle is particularly useful when you realize mid-adjustment that you need to move an entire loop rather than a single point. You can simply switch modes without starting over.

Deleting elements

To remove unwanted geometry:

Delete polygons: Alt+click on a polygon.
Delete vertices: Alt+click on a vertex.
Deleting edgeloops: Hover over a face adjacent to the edgeloop you wish to delete. Hold down Alt, then click+drag across the edgeloop. A red segment appears to track your operation. Release to delete the edgeloop. In the following top images, we start with the second face from the left, then Alt+drag to the leftmost face. Upon releasing, the edgeloop between those two faces deletes. In the bottom before/after images, we begin in the same place, but then we drag right.
Delete temporary vertices and meshes: You can have all manner of stray vertices and temporary geometry on your model. Rather than burn time deleting these individually, simply hold down Ctrl and drag your pointer for any distance off in empty space (shown by the circled square below). All those unwanted points and temporary geometry vanish when you release the mouse.

Extruding vertices

ZBrush offers yet another means of growing topology, this time by manipulating individual vertices. In the following example, a basic retopo mesh sits on the model. Say you want to extend that retopo mesh upward. In the following example, you would place your pointer on the desired vertex, press down Alt, then drag upward. Release the mouse button to create a quad. As the video shows, you can repeat this process.

If you release the Alt key before releasing the mouse button, then your quad splits into two triangles. However, when you repeat the process in an adjacent extrusion the left half forms a quad with the adjacent polygon while the right remains a triangle.

Merging vertices and edges

Vertices and edges automatically merge when moved close together, welding separate topology sections into a continuous mesh. We illustrate this below by dragging two separate vertices into their neighbors, effectively deleting the polygon they defined. The same process applies when dragging edges.

Why you'd use this:

This is useful for connecting separate topology sections you've built independently or for cleaning up overlapping geometry. Simply drag a vertex near another vertex (or an edge to another edge), and they will snap together when sufficiently close. This automatic snapping behavior means you don't need to manually weld points. ZBrush handles the connection for you.