Drying agent. One of the last things that will go on the car. Helps bead the water so the car will dry. Non streaking, non spotting. Leaves a final rinse that is easy for blow off.
Makes for an easy dry off. If you didn't have a drying agent in your car wash the cars would look soaked.
Auto detailers can also use this product to make it easier dry, not just car washes.