It’s a waterproof sheet designed for children which can be placed directly on a shiki-buton for bedwetting prevention. Not only flat-sheet types but also fitted-sheet types are available. These waterproof sheets are made of materials such as polyester, polyethylene and polyurethane, so they easily retain heat in summer. If you use the sheets for your infants who can’t control their body temperature well, you need to pay careful attention. If your child has a sensitive skin, it might be better to lay another sheet on the waterproof sheet.