public float bounciness { get; set; }

Restitution (bounciness) is used to control how "elastic" a collision response is. A value of zero indicates no bounce at all while a value of one indicates perfect elasticity (approximately).

Note: Values higher than one are allowed but will add "energy" to the collision response. Use caution, as this can cause a Rigidbody2D to move quickly without limit, leading to simulation problems.