A foam cannon needs a pressure washer. There is no workaround: it relies on high-pressure water forced through soap solution and a mesh screen to whip in air. Garden hose pressure cannot do it.
A foam gun is the garden-hose version, and it works perfectly well — with thinner foam.
What a cannon needs from a machine
Minimum workable: roughly 1.2 GPM and 1,400 PSI, which is essentially any electric pressure washer sold today. Foam will be modest but real.
Comfortable: 1.6 to 2.0 GPM. This is where foam starts looking like the product videos.
More than enough: 2.5 GPM gas. Thick foam, and considerably more pressure than you want near paint, so you will be careful with the rinse.
The flow figure is the one that matters — PSI vs GPM. If your machine is at the bottom of that range, read foam cannons for electric pressure washers before buying a cannon.
If the car is your only reason to buy a machine
Then honestly: buy a foam gun first. It screws onto a hose, costs a fraction of a machine plus cannon, and gives you most of the actual benefit — floating grit off the paint before a mitt touches it, which is where swirl marks come from.
The foam will be visibly thinner and you will not have a powered rinse. For a weekly wash with a two-bucket method, that is a complete setup. The comparison is in foam cannon vs foam gun.
If you have other cleaning jobs
Then buy the machine for those and treat the cannon as a cheap addition. A driveway, a deck, siding or a fence all genuinely need a pressure washer in a way a car does not — do I need a pressure washer works through that.
In that case buy a gentle machine if the car matters to you, or a mid-range one and commit to using the white 40-degree tip on paint — the car-friendly picks.
The honest cost comparison
Foam gun route: a gun, a bottle of pH-neutral soap, two mitts, two buckets. Cheap, complete, works.
Cannon route: all of the above plus a pressure washer and a cannon. Several times the cost, better foam, a powered rinse, and a machine that also cleans your driveway.
Neither is wrong. The question is whether you have jobs beyond the car.
What a cannon will not do regardless
Replace the contact wash. Foam loosens dirt and lifts grit; road film needs a mitt. Anyone selling a genuinely touchless home wash is overstating what is possible — the sequence that actually works.
