Hello!
In the UK we are somewhat foam obsessed with our soap free foaming products. They cling to the dirt and soften it, you can then blast off with the hose.
If you apply your soap based to the car when its wet, it wont cling and help soften the dirt as well and be fairly reduced in its effectiveness.
Here is a quick demo at the forum i mostly post on
Tyresmoke.Net: Quick Demo with Wonder Foam
You can see the foam being used and being discussed. Generally the higher pressure units create a denser foam.
Great pics @ $30 id love to get my hands on one!
Geoff