Blender Soft Body: Complete Physics Guide

Want a ball that squashes on impact, a balloon that inflates, or jelly that wobbles? Blender soft body is the physics system that delivers that volume-based deformation, and with a few well-understood parameters you can master it on your first simulation.

What Is Soft Body in Blender and When Should You Use It?

Soft body is Blender's simulation engine for objects with volume that deform as they move, collide, or receive force. Unlike other physics systems, it does not treat the object as a rigid solid but as a mass that can compress, stretch, and recover its shape. The official manual recommends it for jelly, balloons, cushions, thick fabrics, and any soft organism that needs bounce and flexibility.

If you have never simulated physics in Blender, it helps to know when each system comes into play. The choice comes down to a single question: should the object deform?

Soft body vs rigid body vs cloth

Rigid body works with non-deformable solids: bricks, boxes, and wheels that collide and bounce without changing shape. It is the system for destruction and stacking, which we already cover in our destruction simulation tutorial. Cloth simulates surfaces without volume: fabrics, flags, and sheets. Soft body fills the space in between: it has volume, but it can deform. A cushion that sinks, a cable that vibrates, or a character with gelatinous parts are soft body cases, not the other two.

The practical rule: if the object keeps its shape, use rigid body; if it is a thin surface, use cloth; if it is a volume that squashes and recovers, use soft body. The three can be combined in a single scene, because each one solves a different kind of material.

How to Create Your First Soft Body

The shortest path to seeing the system work is applying it to a simple object. Select a cube, open the Physics panel in the object properties, and press Soft Body. When you play the animation, the cube falls and deforms when it touches the ground. To make the ground react, add a plane, scale it about five times, and give it collision physics with the Collision button in the same Physics panel.

The basic parameters you will see when expanding the panel are the ones that govern behavior. Mass defines the total mass of the object; Friction controls the resistance against surfaces; Vertex Mass distributes mass per vertex; Bending adds resistance to folding; and Spring Length sets the natural length of the internal springs that hold the shape. With these five adjustments you can already get the typical gelatinous look: lower Spring Length to make the object floppier or raise it to behave almost like a solid.

The classic manual example uses a cube and a plane scaled x5 with frames set to 1 and 150: fall, impact, deformation, and bounce in a single cycle.

The Goal: Pin Vertices to Control the Simulation

One of the most confusing concepts when starting out is the Goal. In the simulation, Blender uses the motion of your animations (F-curves, armatures, parents, or lattices) as a reference; the goal is the final desired position of each vertex according to that animation. The goal weight ranges from 0.0 to 1.0: at 0.0 the vertex obeys only soft body physics, and at 1.0 it follows only the animation. Values in between mix both influences, and that is the trick to controlling the result.

To pin only part of the object, use vertex groups. If you want to hang a balloon from a string, assign a vertex group to the nozzle and give it a high goal weight; the rest of the balloon stays free to deform. The same works for holding one end of a cable or keeping the base of a cushion in place. The Goal's Stiffness and Damping parameters adjust how quickly the vertex returns to its target position and how much it vibrates while doing so.

If your soft bodies float or bounce endlessly, the goal is usually the culprit: check the global goal weight and lower the damping before touching anything else.

Pressure: Balloons and Inflated Objects

For closed objects that must behave as inflated, Blender offers the Exterior and Interior panels with pressure parameters. Exterior pressure pushes inward and interior pressure pushes outward; the pressure volume setting controls how the internal volume responds to size changes. With positive interior pressure, a closed object inflates like a balloon and resists being squashed.

The trick to keeping a balloon from deflating is combining pressure with goal: pin the nozzle with a vertex group and high weight, and leave the rest free to inflate and bounce. Without that pin, the pressure pushes the entire object and the shape is lost. The same principle works for bubbles, soft fruit, or any body with a pressurized interior.

Collisions: Impact Objects and Self Collision

For a soft body to react against other objects, those objects need collision physics. Select each one, go to the Physics panel, and press Collision. By default the soft body collides with everything on the same layer, but you can limit it with a Collision Collection: if you define a collection, the simulation only collides with objects in that collection, avoiding unexpected hits with set dressing or helper meshes.

The most common problem in scenes with several pieces is the mesh passing through itself when folding. The solution is Self Collision, available in its own panel. Its main parameters are Ball Size (the protection radius around each vertex), Stiffness, and Damping, which control how vertices push each other apart. For jelly and very soft masses, raise Ball Size until the mesh stops interpenetrating; the cost in simulation time is small compared to the result.

Stability: Fix Explosions and Jitter

Two failures ruin most first simulations: the mesh explodes and the object vibrates out of control. Both have a fix in the Solver panel. Substeps (minimum and maximum) divide each frame into smaller calculation steps; raising them stabilizes meshes that explode, because the solver detects collisions before the deformation becomes irreversible. The error limit defines the calculation tolerance; lowering it increases precision at the cost of speed.

The object's shape is maintained by the springs in the Edges panel: stiffness and damping for the internal springs, plus the tension, compression, shear, and bending modes, which resist stretching, compression, shearing, and folding. A mesh without enough bending resistance folds like paper; with too much, it loses the soft look.

Do not forget scene scale, which directly affects perceived speed. A body in free fall travels about 5 meters in one second and moves at roughly 10 m/s; if you render at 25 fps, the manual suggests setting Simulation Speed to around 1.3 so the motion looks natural. Adjust that value according to your framerate and the scale of your world.

Baking the Simulation and Rendering

Soft body simulations are recalculated every time you change something in the scene, which makes them unpredictable for rendering. The solution is baking: the system saves the result to cache and reuses it as is, so the motion does not change between tests and you can adjust lights, camera, and materials without recalculating physics.

Performance is the other side of the coin. Soft body is computationally intensive: every vertex with its springs is solved frame by frame, so a dense mesh multiplies simulation time. Start with simple shapes and low resolution, bake the result, and only raise density if the deformation requires it.

Quick Example: A Bouncing Jelly Cube

To see the whole flow in action, build this jelly cube in six steps:

First, create a plane, scale it x5, and give it collision physics. Second, add a cube above it and apply Soft Body in the Physics panel. Third, if you want the top face to stay stable, create a vertex group, enable it as a goal with high weight, and lower the global goal to a medium value. Fourth, enable Self Collision with a moderate Ball Size. Fifth, raise the solver substeps and adjust Simulation Speed. Sixth, bake the simulation and render.

The result is the classic gelatinous block that falls, squashes against the floor, trembles, and recovers its shape. Change Mass and Spring Length to get a firmer or softer material, and repeat the flow with any object that needs realistic deformation.

Conclusion

Blender soft body turns any object with volume into living material: jelly that wobbles, balloons that inflate, cushions that sink. The key is understanding the goal to control the simulation, pressure for inflated objects, self collision to avoid interpenetration, and substeps to tame explosions. With baking, the result stays stable for rendering.

To see these principles applied by experienced artists, explore the curated video tutorials on CGI Academy Hub about physics and animation: they show real workflows that complement what you learned here.