For use with Provent and Durovent rafter vents. Prevents wind driven moisture and cold air infiltration between the rafter and the top of the wall. Reduces energy loss at the attic perimeter. Helps prevent moisture problems on the wall's top plate. Effective for use in new and retrofit applications. Install with rafter vents to maximize attic ventilation performance. Constructed of waterproof and durable polyboard. Meets new energy code requirements for air infiltration. Easy-to-install. Fits most standard and wedge heel 24'' O.C. truss configurations. 10 windblocks per package. For use with Durovent model No. UDV2248 and Provent model No. UPV1448 and PV22480.