It is a mesh material woven from high-strength metal wires (such as stainless steel wires). It gets its name from its hard texture and strong impact resistance. The mesh openings are usually square or diamond-shaped, and it has both protective properties (anti-theft, anti-fall) and permeability (ventilation, light transmission). It is widely used in scenarios such as door and window protection, balcony railings, and insect screens.