Frost King's Foam Vent Plug is used to winterize your crawl space. A quick and easy pressure fit installation can reduce your heating bill and increase the warmth and coziness of your home. Insulating your crawl space during the winter months reduces the risk of freezing pipes. Foam vent plugs are installed from the outside of the home eliminating the need to go inside the crawl space. Foam vent plugs are sized to fit dual-cavity block vents and can be trimmed and shaped with a utility knife for non-standard applications.