An airbrush is a small spray tool that atomises thinned paint into a fine mist, and in puppet work it does one thing nothing else does: it adds soft, gradual colour with no visible edge.
Why it matters
A puppet face in one flat colour reads flat under light. A trace of warmer tone in the cheeks, a subtle shadow under the brow, a darker gradient inside the mouth — these are what make a face read as dimensional from twenty feet away. Brushed on, they would show a hard edge. Airbrushed, they blend into the pile.
On fleece
Fleece takes airbrush colour beautifully because the pile scatters the mist. Thin acrylic paint heavily — thinner than seems reasonable, closer to milk than to cream — and add fabric medium so the cured paint stays flexible instead of stiffening the nap.
On foam
Foam absorbs. Seal it first or the first pass vanishes and the second blotches.
Build in passes
Multiple light coats from eight to ten inches away, letting each flash off. One heavy pass will soak the fabric, spread past where you aimed, and mat the pile down permanently.
Masking
Loose paper or card held slightly off the surface gives a soft-edged mask. Tape pressed flat gives a hard line and will lift fleece pile when it comes off. Almost always you want the loose mask.
The hack: keep a bag of fleece offcuts in the same colours you build in, and test every mix on a scrap first. Airbrush on fleece does not come off.