An armature is an internal wire or jointed skeleton inside a puppet that lets a soft part hold whatever position it is put into.
What it solves
FoamFoam is the structural material most soft puppets are built ... More and fabricFabric is the outer surface of a puppet — the skin, the cl... More have no memory. A tail, an ear, a tentacle or a floppy limb will hang wherever gravity leaves it. An armature inside the part means it stays where you place it, which turns a dead appendage into something that can be posed and can hold an expression.
Aluminium wire
is the standard for this. It bends easily by hand, holds its shape, and does not spring back. It is sold as armature wire in art supply shops in a range of gauges, and it cuts with almost any cutters.
Gauge selection
Thick enough to hold the weight of the part, thin enough to bend without a tool. Two thinner wires twisted together often work better than one thick one — more holding power, easier to shape, and less prone to a single sharp kink.
Metal fatigue is the enemy
Wire bent repeatedly in the same place work-hardens and eventually snaps, inside a finished puppet where you cannot reach it. Use a gauge heavy enough that it is not being flexed to its limit every time, and expect anything moved constantly to need replacing eventually.
Protect the ends
A cut wire end inside a soft part will work its way through the covering and out. Bend the last centimetre back on itself into a loop, or cap it, before the part gets closed up.
Where it shows up
tails, ears, antennae, tentacles, noses, hair, plants, and the fingers of live hand gloves in some builds.
The hack: build the armature so it can be removed if you can. Access is what makes a broken wire a repair rather than a rebuild.