The foam kit is used in combination with a high-pressure washer to give you 2 machines in 1. It can also be used in combination with hose reels. Works great on long hose lengths. The foam kit provides a thick and fine foam that makes the foam "hang" and has time to work on the surface. In addition, the wear and tear the chemistry has on the high-pressure pump and bypass valve is removed by the fact that the soap does not pass through the machine. Fits high-pressure washers that provide a water quantity of between 15 and 22 liters per minute.