A foam cannon or foam gun throws a thick layer of foam onto the car that encapsulates and pre-soaks dirt particles before you touch it with a wash mitt. That significantly reduces the risk of scratching. A foam cannon runs on a pressure washer and gives the thickest, most clingy foam layer; a foam gun attaches to a garden hose and is handy if you do not have a pressure washer.

The quality of your foam depends on three factors: shampoo concentration, water pressure and the air adjustment knob on the cannon. Playing with those three variables gives you the perfect pH-neutral snow layer that clings for minutes and does the work for you.