No one will argue that the soaping effect from using a foam cannon looks cool/pretty. Some car detailers play this visual effect up to make it appear that a foam cannon wash process is superior to washing without one. NOT SO!
Fact is, regardless of the wash method — foam cannon or not — what’s required for complete cleaning of the car’s surface is AGITATION. No soap on the market (that’s actually safe for your car’s paint) will remove dirt on its own. Car soap acts to soften and lift dirt, and prepares it to be removed by whichever wash media you’re using: wash mitt, sponge, microfibre towel, etc. Therefore, using a foam cannon is actually no more effective at cleaning your car’s paint than a regular “bucket wash”.
When foam cannons first became a mainstream tool, some online videos portrayed it as being a touchless wash method. This is only accurate in the case of a very lightly soiled car, meaning one that could be cleaned just as easily using a quick detailing spray – we’re talking about dust here, not dirt that’s actually stuck to the paint.
Bottom line is, don’t be fooled and oooh-and-aaah when you see a car that’s being foamed. It looks impressive no doubt, but it’s more for show than anything else.