..so, what exactly does this snowfoam do? Drag the dirt away with it as it falls away? I've never used it.
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As I believe it, similar to leaving the dishes to soak... lifts dirt away without the need for using a mitt... usually I clean after this and always believe this helps remove any risk of swirls from dirt on the car being caught in the mitt
Bit of light reading:
http://www.autofinesse.co.uk/why-is-snow-foam-important/