Rigidbody.angularDrag

Description

The angular drag of the object.

Angular drag can be used to slow down the rotation of an object. The higher the drag the more the rotation slows down.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    public Rigidbody rb;

    void Start()
    {
        rb = GetComponent<Rigidbody>();
    }

    // Get a wild spin under control when the user
    // presses the spacebar.
    void Update()
    {
        if (Input.GetKeyDown("space"))
            rb.angularDrag = 0.8F;
        else
            rb.angularDrag = 0;
    }
}