The direction of anisotropy. Anisotropic friction is enabled if the vector is not zero.

DynamicFriction2 and staticFriction2 will be applied along frictionDirection2. The direction of anisotropy is relative to the colliders local coordinate system.

	// Make the collider slippery when going forward but not when going sideways
	collider.physicMaterial.frictionDirection2 = Vector3.forward;
	collider.physicMaterial.dynamicFriction2 = 0;
	collider.physicMaterial.dynamicFriction = 1;

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Example() {
        collider.physicMaterial.frictionDirection2 = Vector3.forward;
        collider.physicMaterial.dynamicFriction2 = 0;
        collider.physicMaterial.dynamicFriction = 1;
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Example() as void:
		collider.physicMaterial.frictionDirection2 = Vector3.forward
		collider.physicMaterial.dynamicFriction2 = 0
		collider.physicMaterial.dynamicFriction = 1