Blender Normal Map Baking Extrusion Setting Explained

The Extrusion setting in Blender’s normal map baking process is a ray-casting offset that artificially expands the low-poly mesh's surface outward during the bake. This guide breaks down what the Extrusion setting does, why it is critical for capturing high-poly details, how it differs from Max Ray Distance, and how to choose the ideal value to avoid baking artifacts.

What Does the Extrusion Setting Do?

When baking a normal map using the Selected to Active option, Blender projects rays from the low-poly mesh (Active) toward the high-poly mesh (Selected) to sample surface angles.

If parts of the high-poly model protrude outside the boundaries of the low-poly mesh, standard ray casting will fail to detect them. This results in black spots, missing detail, or severe distortion on the final normal map.

The Extrusion value inflates the low-poly mesh's virtual starting point outward along its vertex normals before firing rays inward. This creates an invisible "cage" around the high-poly object, ensuring all detailed surfaces are captured.

How Extrusion Works in the Ray Casting Process

  1. Mesh Offset: Blender virtually pushes the vertices of the target low-poly object outward by the distance specified in the Extrusion field.
  2. Ray Direction: Rays are cast inward from this expanded boundary toward the center of the mesh.
  3. Detail Capture: As the rays travel inward, they hit the high-poly mesh surface first, recording its orientation vectors into the low-poly normal map image texture.

Extrusion vs. Max Ray Distance

While both settings control how Blender projects rays between meshes, they perform different functions:

  • Extrusion: Defines the starting distance of the rays by extending the low-poly source geometry outward.
  • Max Ray Distance: Defines the maximum distance a ray can travel from its starting point to find the high-poly surface.

Using Extrusion is generally preferred over increasing Max Ray Distance alone, as Extrusion prevents rays from starting inside the high-poly mesh.

  1. Start with Small Increments: Leave Extrusion at 0.000 initially. If your bake has missing details or black artifacts, increase the value in small increments (e.g., 0.01 to 0.05 Blender units).
  2. Match Mesh Scale: The required Extrusion value depends heavily on the scale of your object. Always apply scale (Ctrl + A > Scale) on both objects before baking.
  3. Avoid Over-Extrusion: Setting the Extrusion value too high can cause rays to overlap neighboring geometry (such as fingers on a hand or adjacent mechanical parts), creating severe projection errors and light bleeding.