Rain-X causes the water to form little balls on the windshield instead of flattening out. When water flattens out it acts like a lens to blur and distort your vision making it difficult to see clearly enough to drive safely. With Rain-X there is no lens effect and when you focus on distance objects the little water balls disappear. This is similar to not seeing a screen in a window unless you focus on the nearby screen. Everything looks much clearer and driving is much safer. On my car at about 45 mph the balls climb up the windshield so no wipers are necessary. Under 45 you only need intermittent wipers if at all.