Old crawl space thinking said that air would blow in a vent on one side of a house and blow out of the vent on the other side. But we now know that a house works like a chimney, sucking air in at the lower levels, including in through all of the open crawl space vents, and then this air rises up into the house and escapes out of the upper levels. This open vent to the outside was allowing water and humidity into the home. CleanSpace Vent Covers go over the old, corroded, unsightly vents for a nice clean looking finish. These crawl space vent covers are durable plastic, so they'll never rust, rot, or need paint. The crawlspace vent covers have a foam insulation and gasket material on the inside to seal off the outside air completely.