Covers are used as a waterproof barrier for all non-waterproof diapers. (Fitteds, Prefolds and Flats). Generally they are made out of Polyurethane laminates (PUL), polyester, waterproof nylon, wool and fleece. They can come in many different styles, such as wrap style covers that you fasten with snaps or aplix, or pull-ups that you use like underpants.
 Bummis Super Brite Covers |  Thirsties Diaper Covers |  Thirsties Duo Wrap Covers |
 Llamajama Wool Longies |  Stacinator Luxury Fleece Cover | |