Physics.bounceThreshold  

static var bounceThreshold : float

Description

Two colliding objects with a relative velocity below this will not bounce (default 2). Must be positive.

This value is usually changed in Edit->Project Settings->Physics inspector instead of from scripts.

Physics.bounceThreshold = 1;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        Physics.bounceThreshold = 1;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        Physics.bounceThreshold = 1