Water on Wax: Why It Beads

Wax can protect your paint from scratches and chips, though it also guards against moisture damage. Learn why water rolls right off with Groupon's study of auto wax.

Rather than forming a gloomy puddle on the hood, water beads up attractively on the surface of a freshly waxed car. Wax is hydrophobic, meaning that it does its best to avoid absorbing water (and the paint-damaging acids and other contaminants that may come with it). Wax is so effective because it is (quite literally) water’s polar opposite. Water is made up of polar molecules, which are asymmetrically charged particles that are easily attracted to dirt and metal as well as to each other, whereas wax is decidedly nonpolar. When rain falls on an unwaxed car, the force holding the droplets together is just slightly more than the force adhering it to the car’s surface, causing the water to spread out. If a car has been treated to a coat of wax, its surface becomes much less adhesive and much more like an ice rink covered in banana peels. This leaves the water with nothing to stick to but itself, causing it to scatter into round beads that easily roll right off the surface.

The size of freshly fallen water beads can indicate whether a car is in need of a wax. If droplets are more than half an inch in diameter, then it's time for a fresh coat. In general, cars benefit from an application of fresh wax every three months, though more frequent waxing is required if cars are often driven through harsh or snowy climates or parked in the first two rows at Sea World.