I haven't tried it because I don't typically make layered cakes, but I think you can use Cool Whip Frosting on a 2 layer cake. I wouldn't use it for more than 2 layers. I would also make sure to keep the cake as cool as possible. And you may want to thicken it up a bit with cream cheese (which will change the flavor and consistency). You can also use traditional frosting in between the layers and just frost the outside of the cake with Cool Whip Frosting.