Whatever you use to clean it... I've always used rain-x on the outside on my windshield. It gives you that beading affect like wax does on paint. You can watch little water beads shoot up your windshield and fly off while driving and the water won't "stick" to your windshield. I must admit though I get distracted watching the little water beads shooting to the top of the windshield while driving haha but good stuff I like it!