The Dryer Vent Seal prevents outside elements and air from entering the vent when the dryer is not in use. When the dryer is in use, the dryer exhaust air pressure pushes up the floating damper. The exhaust air escapes from the vent's bottom. When the dryer stops, the damper drops back down to keep outside elements from entering the vent. Made of ABS plastic, the Dryer Vent Seal mounts easily over an existing 4 in vent pipe and can be painted.