A siphon-feed airbrush hangs a bottle beneath the body and uses airflow to pull paint up a tube — the same physics as a perfume atomizer. Big bottles mean long sessions without refilling, which suits base-coating large models and craft work.
The cost is pressure: siphon feed needs several PSI more to lift paint, which fights fine-detail work. Modelers mostly reach for siphon when volume matters more than line width.
See it in context in our airbrushes guides, or explore the tools hands-on in The Bench.