Waterbed Sheets - 8 colors, 5 Sizes Navy Blue Waterbed Sheet Set - Super Twin. Includes Fitted Sheet, Flat Sheet, 2 Pillowcases. 1 Pillowcase with Twin and Super Twin Sets. Top and bottom sheet are attached. Fits mattresses up to 13" deep. Percale. 180-Thread-Count. 50% Polyester, 50% Cotton. Machine Washable.