enter image description here

In the above picture - there are two cubes with boolean difference operation.

The newly created geometry (created by boolean operation) is red - original geometry is grey. (I changed viewport display of the boolean difference object to wire frame so you can see generated geometry clearly).

If this shape is created with geometry nodes - How to identify or select only the red faces - the generated geometry from boolean operation using geometry nodes only?


2 Answers 2


Probably one of the best solutions is to use the node Capture Attribute with a boolean value.

With this you select the faces before the node Mesh Boolean, which remain afterwards.

You can then use this selection, for example, to apply a specific material, or similar.

enter image description here


Since the Mesh Boolean node doesn't output if a face is part of the original mesh or the boolean mesh, we need another way:

$$\text{Method 1 : Material Index}$$

If you just want to change the material for the new parts, you can just set the Material Index of the boolean mesh sources to the desired material's index:

Geometry Nodes Boolean Material



If you want to do something else besides setting the material, like extruding, just use the Material Index node to select the faces:

Geometry Nodes boolean region extrude


Boolean region extruded

If you want to set the material, but still know what faces comes from the boolean operation, you can capture the Material Index attribute to use it after changing the Material Index in the mesh:

Geometry Nodes capturing Material Index

Extruding from captured Material Index attribute


For using Material indexes, you need to have the material slots for the indexes in your object. Ex: if you want to use three indexes (0 to 2), you need three slots:

Material slots

They don't need to be linked to a material.

$$\text{Method 2 : Raycast}$$

You can raycast from the modified mesh to the original with a very small ray length:

  • Ray hit: from original mesh.
  • Ray miss: from boolean operation.

Geometry nodes boolean selection with raycast

Result, extruding from raycast selection:

Boolean extrude using raycast

With raycast, you cannot use multiple indexes unless you raycast all the meshes being used in the boolean operation.


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