How to make the collision force to effect on one object?

Hi, I'm working on a game that i have two cars in there that they colliding each other with another forces applying on them. I want to put a powerup in the game that when the powerup is activated, the affected car become invulnerable to impact. that means when only the other car(only the other car not any other game object) go through the affected car, it can't affect it and it bounce back.(exactly like the affected cars mass is very high!). I try to make the gameobject iskinematic enable when we have oncollisionstay; but I have many other forces in the scene that must affect the car and when the collision occurs they don't works! also, i increase the affected gameobject mass, but my gameobject becomes heavy too in actuating with other objects in the scene. is there any other way(and a clean one!) to do this action? thanks