Stoner Invisible Glass Rain Repellant Washer Fluid Additive - 10 Ounces is designed to turn your washer fluid into rain repellant, which enhances driving visibility and safety in wet weather. It applies more rain repellant each time you spray your windshield and improves the cleaning effectiveness of your windshield washer fluid. Invisible Glass Washer Fluid Additive mixes easily with plain water or can be added to windshield washer fluid. You can add it directly to your reservoir or mix in a separate container before adding. Just add 4-ounces to every 1-gallon of plain water or seasonal washer fluid in reservoir.