Snow foam isn't just foam for show. The thick foam clings to the paintwork, breaks down dirt, and lets it slide off without you touching anything. This removes the heaviest dirt contactlessly, and only then do you pick up the wash mitt.

The trick is in the thick, sticky consistency: the foam draws the dirt in and rinses it away when you blast it off. Without a pre-wash you drag that dirt across the paint during the hand wash, and that's what causes swirl marks.