Diasble collision between exsisting gameObjects and newly created ones

Questions & Answers
1

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I make a game where the robot should hit the cube and then the cube exploids to a lot of small cubes and gets destroyed after some time. The problem is that I do not know how to neglect the collison between newly generated small cubes and all other rigidbodies. I have tried to enable isTrigger for them but does not seem to work. Any ideas?
The code is also included.

private void OnCollisionEnter(Collision collision)
    {
        if (collision.collider.tag == "Obstacle")
        {

            Debug.Log("hit");
            Explosion();
        }
    }
     void Explosion ()
    {
        gameObject.SetActive(false);
        for (int x = 0; x < cubesAmount; x++)
        {
            for (int y = 0; y < cubesAmount; y++)
            {
                for (int z = 0; z < cubesAmount; z++)
                    createPieces(x, y, z);
            }
        }
        Vector3 explPos = transform.position;
        Collider[] colliders = Physics.OverlapSphere(explPos, radius);
        foreach (Collider hit in colliders)
        {
           Rigidbody rb2 = hit.GetComponent<Rigidbody>();
            if (rb2 != null)
            {
                rb2.AddExplosionForce(Random.Range(explosionMin, explosionMax), transform.position, radius);
            }
            if (hit.gameObject.name == "piece")
            {
                //hit.isTrigger = true;
                Destroy(hit.gameObject, 5f);
            }
        }
        

    }
    void createPieces(int x, int y, int z)
    {
        GameObject piece;
        piece = GameObject.CreatePrimitive(PrimitiveType.Cube);
        piece.transform.position = transform.position + new Vector3 (pieceSize * x , pieceSize * y, pieceSize * z); // setting position
        piece.transform.localScale = new Vector3 (pieceSize, pieceSize, pieceSize); //setting scale of the object
        piece.AddComponent<Rigidbody>();
        piece.GetComponent<Rigidbody>().useGravity = true;
        piece.GetComponent<Rigidbody>().mass = pieceSize;
        piece.GetComponent<Renderer>().material = material;
        piece.GetComponent<Collider>().isTrigger = true;
        piece.name = "piece";

    }
        
}
2

A simple approach would be to put each “piece” game object into a different layer during creation and disable collisions for that layer in the collision matrix in project settings:

Would just need to add this line of code before adding the Rigidbody component

 piece.layer = [int layer number];

eg.

piece.layer = 3;