These 30" x 30" Height Warning Signs are made of heavy-duty .080 REFLECTIVE ALUMINUM (EG). Visable for day or nighttime use. Professional-grade screen printed for years of lasting durability. Pre-drilled holes for easy installation. All our Traffic Signs, Parking Signs, Parking Lot Signs, Traffic Warning Signs and Road Work Signs feature rounded corners and are rustproof. (bridge, overpass, viaduct, ceiling height)