In physics, the bounciness of a surface is called the “coefficient of restitution”. The coefficient of restitution is represented as a number between 0 and 1, which defines how much speed an object retains in the opposite direction along the line of impact after a collisionA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a Rigidbody component and is in motion. More info
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In PhysX, the Physic Material asset’s Bounce property has a value of 0–1, which represents the coefficient of restitution.
0 represents a completely inelastic collision (no bounce) 1 represents a perfectly elastic collision (full bounce) A value between 0 and 1 indicates a partially elastic collision with varying degrees of bounciness.
The default Bounce value in Unity is 0.
In physics simulation, you can also define a threshold at which colliders no longer bounce off each other. If two colliding objects have a relative velocity below the defined value, they do not bounce off each other. To configure the bounce threshold, go to the Physics Settings (Edit > Project Settings > Physics) and set the Bounce Threshold to the minimum velocity at which colliders should bounce. This value is set to 2 by default.