Fine wires mesh wire. It can vary from woven, knitted, rolled, sintered or welded wire meshes. Fine galvanized, black annealed low carbon or stainless steel.
Filtration (avoid “smoke and dust” or fragmented particles in the bag)
Cooling (cool down the hot gasses + smother the flame during combustion)
Airflow (distribute the air when the air bag goes off)
Sealing and resist heat shock (mesh does not melt due to high heat)