The first armor build guide gives the glue rule in one line: contact cement, coat both faces, wait tacky, join once, do not reposition. Four instructions, and each one is the physics doing its job. Worth taking apart, because "what glue for EVA foam" has one answer that carries most of the craft's seams with it, and the same four words explain why armor gets glued the way it does and how to fix the seams that fail anyway.
Contact cement is a solvent-borne adhesive that works differently from wood glue or CA: each surface gets coated separately, the solvent flashes off while you wait for tack, and the two coated faces develop the bond the instant they meet in full area. There is no drying-after-clamping stage, because the chemistry that matters happened before contact. Curved armor exploits that directly: try to clamp a wrapped pauldron seam while a slow-cure glue sets, and the geometry loses, the cement's meet-and-hold lets a curved join go down once, under your hands, at full strength-building area from the first second.
The flip side of instant bonding is that repositioning is off the table: pull apart a fresh contact join and the foam's skin often goes with it. The craft's answer is preparation, dry-fit the pieces first, mark the alignment with a light line (the guide's templates trace in white marker), then make the join deliberately. Flexibility is the other property that matters after contact: the cured film flexes with the foam, which is why the same logic returns at the paint stage of the guide, a rigid paint cracks at every bend, and a rigid glue does the same at a seam.
The guide's fixes table names the two usual cases. A seam cracking at a flex point usually means the joint was starved (too thin a coat on one face) or the seam has no reinforcement, the fix is re-gluing the full face and backing the seam with fabric or a thin foam strip. Paint cracking over bending foam is the rigid-paint lesson, fixed by a flexible primer system and lighter coats. Both fixes are cheap at a workbench and expensive at a con; the bench sheet prints the check rows for that reason.
The catches the guide names, named here too: contact cement is solvent-based, so it wants outdoors or a ventilated room; and before any heat-forming near a bonded piece, read the glue's temperature rating, the foam resets from one overheat, the bond may not.
Dry-fit twice, join once. Hang the mask. — the workshop crew