The Master Flow Foundation Vent Cover is an essential vent opening shield to protect your home by reducing frozen pipes' risk in your crawl space. The crawl space vent cover will also help with insulation issues and moisture control by deterring debris' entry, such as leaves and rodents, into your crawl space. Made from aluminum, these foundation vent covers eliminate rust. They are easy to mount over most 16 inch x 8 inch foundation vents. One package contains 2 covers and 2 springs.