Soft bodies
Squishy, jiggly objects that deform on impact, spring back, and hold their volume while they do it.
A soft body takes a solid mesh and lets it wobble, dent and bounce like jelly, rubber or a stress ball. Cloth is a thin surface. A soft body has insides, and tries to keep both its shape and its volume as it is squashed.
What makes it squishy
The Soft Body Sim node turns an incoming mesh into a deformable body and runs it on the GPU. Two things keep it feeling solid.
Shape springs along the mesh edges resist stretching and tearing, so the surface holds together. Volume and pressure keep the interior from collapsing: squash one side and the rest bulges out, like air trapped in a balloon. High pressure gives an inflated, bouncy feel, low pressure a denser, doughier one.
Wire a mesh into the node, drop it into the simulation and press play. The mesh deforms when it hits the floor or a collider, then settles back toward its original shape.
Start with a mesh that has an even, moderate amount of detail. A very sparse mesh has little to deform, and an extremely dense one costs more to cook every frame. A medium-resolution sphere or character is a good first test.
Putting it in a scene
Soft bodies live in the same simulation world as everything else. Feed the soft body, any Rigid Body Sim objects and the colliders into the simulation and they all interact in one solve, so a soft ball bounces off a static floor and gets knocked around by falling rigid blocks.
Add gravity, ground and obstacles the usual way (see Forces & collisions). Wind and attractors from a Force Field push on a soft body like anything else.
| Parameter | Type | Default | What it does |
|---|---|---|---|
input | Geometries or Primitives | — | Geometry with mesh topology (edges + triangles for constraints), or a 2D shape |
pin_group | String | "" | Point group name for pinned vertices (inv_mass = 0) |
iterations | Number | 10 | Solver iterations per frame (higher = stiffer) |
stretch_compliance | Number | 0 | Stretch compliance (0 = rigid, higher = stretchy) |
volume_compliance | Number | 0 | Volume compliance (0 = incompressible, higher = compressible) |
shape_stiffness | Number | 0.100 | Shape matching stiffness (0 = disabled, 1 = rigid shape recovery) |
damping | Number | 0.010 | Velocity damping (0 = none, 1 = full) |
strength | Number | 1 | Effect strength / wet-dry (0 = no effect, 1 = full). Editable, wirable, keyframable. |
Tuning the feel
Four controls shape the personality of the body.
Stiffness. High values snap firmly back to the rest shape, like rubber; low values stay floppy and slow to recover, like memory foam.
Pressure / volume, how hard the interior resists being squashed. This is the dial that separates a beach ball from a bean bag.
Damping, how quickly the jiggle dies down. Low damping wobbles for a long time; high damping settles fast.
Iterations / substeps, set on the simulation. Raise these if a fast or heavy body looks rubbery, passes through colliders, or jitters. They cost more to cook, so push them only as far as the shot needs.
A soft body that explodes, sinks through the floor or quivers in place is usually moving too fast for the solver to keep up. Increase substeps first, then iterations, and check that the collider is a solid surface rather than a thin shell.
Soft bodies against the alternatives
A thin flapping surface, a flag or a cape, is Cloth. A body that keeps a fixed shape and only rotates and slides is a rigid body, Rigid bodies. Strands, hair, rope or grass, are Hair. Soft bodies sit between them: volume preserved, shape still deformable.