Control Particle Density with Vertex Groups in Blender

Using vertex groups to control particle density allows you to precisely distribute particles across specific areas of a 3D mesh. This guide explains how to create a vertex group, define distribution weights using Weight Paint mode, and link the group to your particle system's density settings in Blender.

Step 1: Create a Particle System

  1. Select your target mesh in the 3D Viewport.
  2. Navigate to the Particle Properties tab (the icon with three connected dots) in the Properties panel on the right.
  3. Click the + button to add a new particle system.
  4. Choose either Emitter (for scattered objects like debris or rain) or Hair (for grass, fur, or foliage).

Step 2: Create and Paint the Vertex Group

  1. With your mesh selected, switch from Object Mode to Weight Paint mode using the mode dropdown in the top-left corner of the 3D Viewport.
  2. Selecting Weight Paint mode automatically creates a new vertex group in the Object Data Properties tab (green triangle icon).
  3. Use the brush to paint directly on your mesh:
    • Red (Weight 1.0): Maximum particle density.
    • Yellow/Green (Weight 0.5): Moderate particle density.
    • Blue (Weight 0.0): No particles will spawn.
  4. You can adjust the brush Weight, Radius, and Strength in the top toolbar to blend edges and control gradients smoothly.

Step 3: Assign the Vertex Group to Particle Density

  1. Switch back to Object Mode.
  2. Go back to the Particle Properties tab.
  3. Scroll down and expand the Vertex Groups dropdown panel.
  4. Locate the Density field and click on the empty box.
  5. Select the vertex group you just painted (usually named Group by default).

The particles will instantly reposition to appear only on the weighted areas of the mesh.

Step 4: Fine-Tune the Distribution

  • Invert Density: Click the double-arrow icon next to the Density field to flip the distribution so particles spawn only on unpainted areas.
  • Live Adjustments: Return to Weight Paint mode with the particle system visible. As you paint or erase weights, the particle distribution will update in real time in the viewport.
  • Particle Count: If the density feels too low in the painted areas, increase the Number value under the Emission section of the Particle Properties tab.