VentBlock and VentBlock+ are polyethylene panels that provide a fast, clean and effective way to seal foundation vents in a closed crawlspace. The “plus” version features a screen backing to restrict rodent entry. These units fit a traditional 8×16-inch opening (actual size 8.25 x 16.25 x 1 inch). They can be trimmed to fit a smaller size if needed, and an optional seal is available for edges. Simply install by press-fitting VentBlock or VentBlock+ to the back side of the existing foundation vent. Caulk around the edges for a better seal and a better hold against wind.