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# particleBounce

The restitution coefficient of each particle in the system. Animatable.

```
var particleBounce: CGFloat { get set }
```

## Discussion

Restitution determines the amount of energy gained or lost in a collision. (To define collision behavior, see the [`colliderNodes`](/documentation/SceneKit/SCNParticleSystem/colliderNodes) property.)

A value of `1.0` specifies that a particle loses no energy in a collision (for example, a particle that falls from a certain height onto a flat surface bounces back to the same height). Larger values specify energy gained, and smaller values specify a loss of energy. A value of `0.0` prevents particles from bouncing. You can randomize the bounce factors of particles in the system with the [`particleBounceVariation`](/documentation/SceneKit/SCNParticleSystem/particleBounceVariation) property.

The default value is `0.7`.

You can animate changes to this property’s value. See [Animating SceneKit Content](/documentation/SceneKit/animating-scenekit-content).

---

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