Steel arch frames offer high strength and long life, typically hot-dip galvanized for corrosion resistance. Steel handles heavy snow loads and supports wide spans. Aluminum arch frames are lightweight and inherently corrosion-resistant, featuring easy installation with modular connections. Aluminum works well in coastal areas where salt spray accelerates steel corrosion. Compare initial cost, expected lifespan, and maintenance requirements when selecting. Some greenhouses combine both materials using steel for main structural members and aluminum for secondary framing.