RGS Labs Inc. CU4 technology makes short work of the toughest stains! The perfect companion for the Car & Home, CU4 interior treatment deodorizes, removes stains and protects upholstery, fabric and carpet.. without wasting time or water! CU4 eliminates both set-in stains and stubborn odors! With CU4 Interior Treatment, you don't cover stains.. you remove them! You don't mask odors.. you eliminate them! And it just smells clean.