A Foam Cannon goes on a water blaster and gives real thick fine foam, like thick shaving cream. Our favorite is the Big Mouth, it gives great foam, has heaps of adjustments, a wide opening to make it easy to fill without spilling soap everywhere, and has a cool clear bottle. All the crew had older foam cannons and we all got new Big Mouths when they came out and we love them. If You have a smaller water blaster you will probably need an adapter. We have adapters for all main brands of water blasters, some of these are currently "SOLD OUT" but we are expecting these to be available this Wednesday. If you have a very high pressure industrial water blaster you are better to go with the TORQ Pro, but for most people the Big mouth is the go.
Foam guns like the R1 and Blaster 6 go on a normal hose. These are handy as they are real quick to use, you don't have to have a water blaster, but they foam differently. You don't get the thick fine foam you get with the Big Mouth the Soap is bigger bubbles, more like bubble bath than shaving cream. Of the two the R1 is cheaper and works great, but the Blaster 6 is better quality and will use a little less soap.
Tip for Detailers and fleets: If you are using these for a work environment we recommend getting 2, so if someone drives over one you have a backup.