Control Edge Spring Elasticity in Blender Soft Body

Controlling edge spring elasticity in a Blender soft body simulation allows you to define how an object stretches, compresses, and bounces under dynamic forces. By adjusting the soft body Edge settings—specifically Pull, Push, Damp, and Bending—along with custom vertex weight maps, you can accurately simulate materials ranging from stiff rubber to gelatinous structures.

1. Enable Soft Body Edges

To begin modifying spring mechanics, ensure your mesh has soft body physics enabled and edge calculations active:

  1. Select your mesh and navigate to the Physics Properties tab in the Properties panel.
  2. Enable Soft Body.
  3. Expand the Edges subpanel and ensure the checkbox is enabled. This treats every edge of the mesh as a physical spring connecting the vertices.

2. Adjust Core Spring Parameters

The core elasticity of the edges is governed by the following settings within the Edges panel:

  • Pull: Sets the spring resistance to stretching. A value of 0.0 allows edges to stretch infinitely with no restoring force, creating extreme elasticity. A value approaching 0.99 makes the springs very stiff, resisting any elongation.
  • Push: Sets the spring resistance to compression. Lower values allow the mesh to squish easily, while higher values force edges to maintain their original length when compressed.
  • Damp: Controls the friction within the spring network. Low values (near 0.0) produce high elasticity and prolonged bouncing, while higher values absorb kinetic energy rapidly, stopping oscillations almost immediately.
  • Bending: Creates virtual spring connections between non-adjacent vertices across faces. Increasing this prevents the surface from folding too sharply and maintains structural volume.
  • Plasticity: Determines permanent deformation. When set to 0.0, springs return completely to their rest length. Higher values cause springs to retain their stretched or compressed state once a force threshold is exceeded.

3. Localize Elasticity with Vertex Groups

To make certain areas of a mesh more elastic than others:

  1. Switch to Weight Paint mode on your mesh.
  2. Paint a new Vertex Group (values closer to 1.0 represent high stiffness; values closer to 0.0 represent high elasticity).
  3. Return to the Physics Properties > Soft Body > Edges panel.
  4. Under the Springs field, select your newly created Vertex Group to drive the elasticity distribution across the mesh.

4. Fine-Tune Solver Settings

High elasticity can sometimes cause instability or exploding meshes. To stabilize elastic springs:

  • Open the Soft Body Solver panel.
  • Increase Min Step and Max Step (e.g., from 10 to 20 or higher) to calculate more sub-steps per frame, ensuring the springs resolve accurately without numerical instability.