The Explode modifier is used to alter the mesh geometry by moving/rotating its faces in a way that roughly tracks particles emitted by that object, making it look as if the mesh is being exploded (broken apart and pushed outward).
For this modifier to have any visible effect, there needs to be a particle system on its object. That particle system will control how the mesh is exploded.
Both the number of emitted particles and number of faces determine how granular the Explode modifier is. More faces and more particles will mean more individual pieces.
Here is a demo blend-file showing a cube with a particle system and Explode modifier.
The Explode modifier must come after the Particle System one in the modifier stack, in order for the former to get required data from the later.
- Vertex Group
Vertices in this group may not be affected by the Explode modifier. Vertices with full weight are not affected at all, while vertices with less weight have a higher chance of being affected.
Vertices with null weight will be treated like those which do not belong to the group at all, and explode normally.
Inverts the influence of the selected vertex group, meaning that the group now represents vertices that will not be deformed by the modifier.
The setting reverses the weight values of the group.
Clean vertex group edges. Depending on the weights assigned to that vertex group, either completely protect those faces from being affected by the Explode modifier (which would happen if the faces had a weight value of 1), or completely remove protection from those faces (which would happen if the faces had a weight value of 0).
- Particle UV
If set, the U value of the coordinates in that UV map will be overwritten with the age of the particle attached to the matching mesh face (in proportion, from 0 for not yet born particles, to 1 for dead ones).
The V value is set to a constant 0.5 value.
This allows e.g. to make the color of a fragment (face) vary during it 'explosion' phase, by using a texture with a gradient of colors along its U axis.
- Cut Edges
Split the mesh in pieces based on location of emitted particles, instead of using existing faces. This will typically give a splitting that appears more random.
Show faces when their attached particles are unborn.
Show faces when their attached particles are alive.
Show faces when their attached particles are dead.
Scale each face using the size of its attached particle, once that particle is alive.
Refresh data in the Explode modifier.