Often you see Youtubers foam the car directly before the wash – I say this is not needed and can lead to bad techniques.
What does foam do?
It allows for two things, longer dwell times and some resistance against product drying out, which makes it beneficial in hot weather.
Foaming means that you use air to create a foam out of a water and cleaner mixture. Not all types of cleaners contain the correct chemicals to actually foam and some even contain inhibitors to not foam at all (some fabric cleaners for example, to not foam up in the sewage tank of the extractor).
The foam is less dense and sticks to the paint, which is why it is usually better to foam a dry car (also because the standing water would further dilute the cleaner). The chemicals in the foam now have more time to work on the dirt in hotter climates so the chemical can stay on the paint for longer. Exceptions for this are if the car is either full of mud or hot and you want it to cool down first.
Foam Consistency
A wet foam that actually pulls down in a few minutes is mostly what cleans best as with more air the amount of chemicals with surface contact decreases. A too air-y foam (As in shaving cream foam) might look good on the social media of your choice but actually cleans worse then a wet foam.
Why is foam not needed for washing?
Often people mix up foaming with pre-washing. A real pre-wash can have foam, but ends with a rinse (from pressure washer if you have one, but even just straight from the hose works), no matter what. This significantly increases the safety of any method by removing dirt before the contact step.
Using foam often results in people forgetting to properly wash out the mitt. Using one mitt without cleaning it out on a car is not a safe method. Foam is fine if you use it, but it doesn’t eliminate debris which is what actually scratches the paint. The foam can hide the dirt, and you can no longer have proper control with the mitt to prevent damage.
Order of steps for foaming during a wash
- BAD: Rinse, then foam, then contact wash
- GOOD: Pre-wash (foam or not), then rinse, then contact wash
When is foaming helpful?
There is a good reason for Foam on other parts of the cleaning process other than washing paint and wheels. For leather and especially open porous leather, foam is much appreciated as it is dryer vs. using a wet cleaner so the moisture can not penetrate too deep into the material. The dryness of foam is much appreciated there where on other surfaces a wetter approach will give the dirt more place to be.