This washer fluid additive works! Absolutely the best thing to add to your washer fluid if you get a lot of bugs or road grime, as it boosts the effectiveness of your washer fluid. Film covered windshields will be a thing of the past as soon as you add the P21S windshield wash booster to your favorite washer fluid. Increase the cleaning power of your current windshield washer fluid. It helps improve visibility, which helps you drive safer in poor weather conditions.