The Thule WindDiffuser T-Slot Cover Strips are textured rubber strips that press into the t-slot on Thule AeroBlade load bars and the Rapid Aero load bars.  The textured surface is wind tunnel tested to disrupt the airflow better than a smooth surface which greatly reduces wind noise.  The 60 inch strip can be cut down with a sissors to fit all Thule bar lengths.  The WindDiffuser T-Slot Cover Strip is an excellent upgrade for Thule's Rapid Aero load bars.