Rain?X Windshield Repair Kit helps you minimize the appearance and stop the spread of chips and cracks in your windshield. It removes air from the break, fills it with durable resin and makes it even stronger than before. For best results, repairs should be made as soon as possible after the damage occurs and before the break is contaminated by dirt or water. The kit works best on round damage not more than one inch in diameter, and cracks not longer than 12 inches. It will not repair damage to more than one layer of glass.