Car magnet signs are made of a thin magnetic material that is about as thick as a piece of heavy construction paper. One side sticks to your metal truck door and the other side is used for printing. We print all of our car magnetics digitally in full color and at a very high resolution.Car door magnet installation tip: To guarantee maximum hold, clean the surface area and allow it to dry before placing your car door magnet. Also, make sure the car door magnet placement is flat with no air pockets. Car door magnets only stick to metal. Not aluminum and not bondo. These are examples of our most popular sizes. Any size or shape car magnets can be made to your specification.