A foam bath may be a luxury for us humans but when washing delicate surfaces such as the painted surfaces of your car, the foaming action actually allows you to quickly saturate the entire car and enables the car shampoo to work its magic on the dried-up bugs or ingrained grime prior to being pressure washed off.

As most car-detailing gurus would agree, when paired with a two-bucket method, this pre-washing step is crucial to not only save you time with the wash mitt, but also reduces the amount of scratches on the clearcoat.

The foam jet attachments such as the Karcher FJ6 Foam Jet or FJ10C Foam Nozzle (that allows for rapid switching between different detergents with its quick-change system) isn't just limited to washing your vehicles, it can similarly be used on outdoor furnitures or even outside walls with a suitable universal cleaning detergent such as the Karcher Universal Cleaner.

But my pressure washer already has a detergent dispenser why do I need a foam jet attachment?
While many Karcher pressure washer have a built-in detergent dispenser, they only work at low-pressure setting on the spray wand to quickly spray a layer of detergent on the surfaces to be cleaned.

Unless you're using it on a fairly flat surface such as the patio floor, the dispenser will not generate a blanket of foam to sit and saturate the grime and dirt on vertical surfaces.

As a side note, if you do use the detergent dispenser, be sure to use pressure washer-safe detergents as certain types of caustic chemical cleaners can actually damage the pressure washer's seals and cause it to leak.